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/repo/release.go

@@ -6,7 +6,6 @@ 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/to"
 
@@ -97,7 +96,6 @@ func init() {
 }
 
 func CreateReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called CreateReleasesFn")
 	args := req.GetArguments()
 	owner, err := params.GetString(args, "owner")
 	if err != nil {
@@ -136,14 +134,13 @@ func CreateReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 		IsPrerelease: isPreRelease,
 	})
 	if err != nil {
-		return nil, fmt.Errorf("create release error: %v", err)
+		return to.ErrorResult(fmt.Errorf("create release error: %v", err))
 	}
 
-	return mcp.NewToolResultText("Release Created"), nil
+	return to.TextResult("Release Created")
 }
 
 func DeleteReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called DeleteReleaseFn")
 	args := req.GetArguments()
 	owner, err := params.GetString(args, "owner")
 	if err != nil {
@@ -164,14 +161,13 @@ func DeleteReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToo
 	}
 	_, err = client.DeleteRelease(owner, repo, id)
 	if err != nil {
-		return nil, fmt.Errorf("delete release error: %v", err)
+		return to.ErrorResult(fmt.Errorf("delete release error: %v", err))
 	}
 
 	return to.TextResult("Release deleted successfully")
 }
 
 func GetReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called GetReleaseFn")
 	args := req.GetArguments()
 	owner, err := params.GetString(args, "owner")
 	if err != nil {
@@ -192,14 +188,13 @@ func GetReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolRe
 	}
 	release, _, err := client.GetRelease(owner, repo, id)
 	if err != nil {
-		return nil, fmt.Errorf("get release error: %v", err)
+		return to.ErrorResult(fmt.Errorf("get release error: %v", err))
 	}
 
 	return to.TextResult(slimRelease(release))
 }
 
 func GetLatestReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called GetLatestReleaseFn")
 	args := req.GetArguments()
 	owner, err := params.GetString(args, "owner")
 	if err != nil {
@@ -216,14 +211,13 @@ func GetLatestReleaseFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.Call
 	}
 	release, _, err := client.GetLatestRelease(owner, repo)
 	if err != nil {
-		return nil, fmt.Errorf("get latest release error: %v", err)
+		return to.ErrorResult(fmt.Errorf("get latest release error: %v", err))
 	}
 
 	return to.TextResult(slimRelease(release))
 }
 
 func ListReleasesFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("Called ListReleasesFn")
 	args := req.GetArguments()
 	owner, err := params.GetString(args, "owner")
 	if err != nil {
@@ -233,18 +227,7 @@ func ListReleasesFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTool
 	if err != nil {
 		return to.ErrorResult(err)
 	}
-	var pIsDraft *bool
-	isDraft, ok := args["is_draft"].(bool)
-	if ok {
-		pIsDraft = new(isDraft)
-	}
-	var pIsPreRelease *bool
-	isPreRelease, ok := args["is_pre_release"].(bool)
-	if ok {
-		pIsPreRelease = new(isPreRelease)
-	}
-	page := params.GetOptionalInt(args, "page", 1)
-	pageSize := params.GetOptionalInt(args, "per_page", 20)
+	page, pageSize := params.GetPagination(args, 20)
 
 	client, err := gitea.ClientFromContext(ctx)
 	if err != nil {
@@ -252,14 +235,14 @@ func ListReleasesFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTool
 	}
 	releases, _, err := client.ListReleases(owner, repo, gitea_sdk.ListReleasesOptions{
 		ListOptions: gitea_sdk.ListOptions{
-			Page:     int(page),
-			PageSize: int(pageSize),
+			Page:     page,
+			PageSize: pageSize,
 		},
-		IsDraft:      pIsDraft,
-		IsPreRelease: pIsPreRelease,
+		IsDraft:      params.GetOptionalBoolPtr(args, "is_draft"),
+		IsPreRelease: params.GetOptionalBoolPtr(args, "is_pre_release"),
 	})
 	if err != nil {
-		return nil, fmt.Errorf("list releases error: %v", err)
+		return to.ErrorResult(fmt.Errorf("list releases error: %v", err))
 	}
 
 	return to.TextResult(slimReleases(releases))