Simplify codebase (#195)

Net **-650 LOC** by removing duplication and dead noise. All tests pass.

### Duplication & helpers
- Extracted shared slim helpers (`UserLogin`, `UserLogins`, `LabelNames`, `BodyWithAttachments`, `UserDetail`, `Repo`/`Repos`, `Label`/`Labels`) into `pkg/slim`. Deleted the 4 copies that lived in `issue/`, `pull/`, `search/`, `repo/` (plus duplicate `slimUserDetail`/`slimRepo`/`slimLabels` across packages).
- Added `params.GetOptionalBoolPtr` and `params.GetOptionalStringPtr`. Replaced 18 awkward `new(localVar); if !ok { = nil }` patterns across `repo/`, `pull/`, `issue/`, `label/`, `milestone/`, `search/`.
- Extracted `pullRequestReviewerFn` for the 99%-identical `createPullRequestReviewerFn`/`deletePullRequestReviewerFn` pair.

### Dead code & noise
- Deleted **122** `log.Debugf("Called X")` narration lines (`zap.AddCaller` already records the caller) and pruned 19 unused `log` imports.
- Removed the unused `log.Logger` wrapper; the mcp-go server now uses `log.Default().Sugar()` directly (matches `util.Logger`).
- Deleted dead `s.DeleteTools("")` — confirmed no-op in mcp-go.
- Stripped WHAT-narration comments per project guidance.

### Correctness & consistency
- Fixed `log.Errorf(err.Error())` format-string bug in `pkg/to/to.go` — a `%` in the error would have been interpreted as a directive.
- Standardized `to.TextResult`/`to.ErrorResult` usage; `release.go`, `tag.go`, `branch.go` were bypassing the helpers in 9 sites (skipping the wrapper's debug/error logging).
- Made `params.GetString` reject empty strings; dropped 21 redundant `err != nil || x == ""` checks in `operation/actions/`.
- Replaced raw `args["org"].(string)` in `ListOrgReposFn` with `params.GetString` to match the rest of the codebase.

### Performance
- **Cached `*gitea.Client` by host+token via `sync.Map`** + shared `*http.Transport` via `sync.Once` for both SDK and raw REST paths. Eliminates the SDK's `/api/v1/version` preflight on every tool call and enables connection keep-alive across requests.
- Gated `to.TextResult` debug log behind `flag.Debug` to skip the `string(bytes)` allocation when debug is off.
- Hoisted `8192` and `60s` magic numbers in `pkg/gitea/rest.go` into named constants.

---
This PR was written with the help of Claude Opus 4.7

---------

Co-authored-by: silverwind <silv3rwind@gmail.com>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/195
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

operation/label/label.go

@@ -6,8 +6,8 @@ import (
 
 	"gitea.com/gitea/gitea-mcp/pkg/annotation"
 	"gitea.com/gitea/gitea-mcp/pkg/gitea"
-	"gitea.com/gitea/gitea-mcp/pkg/log"
 	"gitea.com/gitea/gitea-mcp/pkg/params"
+	"gitea.com/gitea/gitea-mcp/pkg/slim"
 	"gitea.com/gitea/gitea-mcp/pkg/to"
 	"gitea.com/gitea/gitea-mcp/pkg/tool"
 
@@ -108,7 +108,6 @@ func labelWriteFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolRe
 }
 
 func listRepoLabelsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called listRepoLabelsFn")
 	owner, err := params.GetString(req.GetArguments(), "owner")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -133,11 +132,10 @@ func listRepoLabelsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("list %v/%v/labels err: %v", owner, repo, err))
 	}
-	return to.TextResult(slimLabels(labels))
+	return to.TextResult(slim.Labels(labels))
 }
 
 func getRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called getRepoLabelFn")
 	owner, err := params.GetString(req.GetArguments(), "owner")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -159,11 +157,10 @@ func getRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTool
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("get %v/%v/label/%v err: %v", owner, repo, id, err))
 	}
-	return to.TextResult(slimLabel(label))
+	return to.TextResult(slim.Label(label))
 }
 
 func createRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called createRepoLabelFn")
 	owner, err := params.GetString(req.GetArguments(), "owner")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -199,11 +196,10 @@ func createRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallT
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("create %v/%v/label err: %v", owner, repo, err))
 	}
-	return to.TextResult(slimLabel(label))
+	return to.TextResult(slim.Label(label))
 }
 
 func editRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called editRepoLabelFn")
 	owner, err := params.GetString(req.GetArguments(), "owner")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -217,18 +213,12 @@ func editRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 		return to.ErrorResult(err)
 	}
 
-	opt := gitea_sdk.EditLabelOption{}
-	if name, ok := req.GetArguments()["name"].(string); ok {
-		opt.Name = new(name)
-	}
-	if color, ok := req.GetArguments()["color"].(string); ok {
-		opt.Color = new(color)
-	}
-	if description, ok := req.GetArguments()["description"].(string); ok {
-		opt.Description = new(description)
-	}
-	if isArchived, ok := req.GetArguments()["is_archived"].(bool); ok {
-		opt.IsArchived = &isArchived
+	args := req.GetArguments()
+	opt := gitea_sdk.EditLabelOption{
+		Name:        params.GetOptionalStringPtr(args, "name"),
+		Color:       params.GetOptionalStringPtr(args, "color"),
+		Description: params.GetPresentStringPtr(args, "description"),
+		IsArchived:  params.GetOptionalBoolPtr(args, "is_archived"),
 	}
 
 	client, err := gitea.ClientFromContext(ctx)
@@ -239,11 +229,10 @@ func editRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("edit %v/%v/label/%v err: %v", owner, repo, id, err))
 	}
-	return to.TextResult(slimLabel(label))
+	return to.TextResult(slim.Label(label))
 }
 
 func deleteRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called deleteRepoLabelFn")
 	owner, err := params.GetString(req.GetArguments(), "owner")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -269,7 +258,6 @@ func deleteRepoLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallT
 }
 
 func listOrgLabelsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called listOrgLabelsFn")
 	org, err := params.GetString(req.GetArguments(), "org")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -290,11 +278,10 @@ func listOrgLabelsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("list %v/labels err: %v", org, err))
 	}
-	return to.TextResult(slimLabels(labels))
+	return to.TextResult(slim.Labels(labels))
 }
 
 func createOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called createOrgLabelFn")
 	org, err := params.GetString(req.GetArguments(), "org")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -325,11 +312,10 @@ func createOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("create %v/labels err: %v", org, err))
 	}
-	return to.TextResult(slimLabel(label))
+	return to.TextResult(slim.Label(label))
 }
 
 func editOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called editOrgLabelFn")
 	org, err := params.GetString(req.GetArguments(), "org")
 	if err != nil {
 		return to.ErrorResult(err)
@@ -339,18 +325,12 @@ func editOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTool
 		return to.ErrorResult(err)
 	}
 
-	opt := gitea_sdk.EditOrgLabelOption{}
-	if name, ok := req.GetArguments()["name"].(string); ok {
-		opt.Name = new(name)
-	}
-	if color, ok := req.GetArguments()["color"].(string); ok {
-		opt.Color = new(color)
-	}
-	if description, ok := req.GetArguments()["description"].(string); ok {
-		opt.Description = new(description)
-	}
-	if exclusive, ok := req.GetArguments()["exclusive"].(bool); ok {
-		opt.Exclusive = new(exclusive)
+	args := req.GetArguments()
+	opt := gitea_sdk.EditOrgLabelOption{
+		Name:        params.GetOptionalStringPtr(args, "name"),
+		Color:       params.GetOptionalStringPtr(args, "color"),
+		Description: params.GetPresentStringPtr(args, "description"),
+		Exclusive:   params.GetOptionalBoolPtr(args, "exclusive"),
 	}
 
 	client, err := gitea.ClientFromContext(ctx)
@@ -361,11 +341,10 @@ func editOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTool
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("edit %v/labels/%v err: %v", org, id, err))
 	}
-	return to.TextResult(slimLabel(label))
+	return to.TextResult(slim.Label(label))
 }
 
 func deleteOrgLabelFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called deleteOrgLabelFn")
 	org, err := params.GetString(req.GetArguments(), "org")
 	if err != nil {
 		return to.ErrorResult(err)