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/user/user.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"
 
@@ -17,62 +17,34 @@ import (
 )
 
 const (
-	// GetMyUserInfoToolName is the unique tool name used for MCP registration and lookup of the get_me command.
 	GetMyUserInfoToolName = "get_me"
-	// GetUserOrgsToolName is the unique tool name used for MCP registration and lookup of the get_user_orgs command.
-	GetUserOrgsToolName = "get_user_orgs"
-
-	// defaultPage is the default starting page number used for paginated organization listings.
-	defaultPage = 1
-	// defaultPageSize is the default number of organizations per page for paginated queries.
-	defaultPageSize = 30
+	GetUserOrgsToolName   = "get_user_orgs"
 )
 
-// Tool is the MCP tool manager instance for registering all MCP tools in this package.
 var Tool = tool.New()
 
 var (
-	// GetMyUserInfoTool is the MCP tool for retrieving the current user's info.
-	// It is registered with a specific name and a description string.
 	GetMyUserInfoTool = mcp.NewTool(
 		GetMyUserInfoToolName,
 		mcp.WithDescription("Get current user"),
 		mcp.WithToolAnnotation(annotation.ReadOnly("Get current user information")),
 	)
 
-	// GetUserOrgsTool is the MCP tool for listing organizations for the authenticated user.
-	// It supports pagination via "page" and "per_page" arguments with default values specified above.
 	GetUserOrgsTool = mcp.NewTool(
 		GetUserOrgsToolName,
 		mcp.WithDescription("List current user's organizations"),
 		mcp.WithToolAnnotation(annotation.ReadOnly("Get user organizations")),
-		mcp.WithNumber("page", mcp.Description(params.PageDesc), mcp.DefaultNumber(defaultPage)),
-		mcp.WithNumber("per_page", mcp.Description(params.PaginationDesc), mcp.DefaultNumber(defaultPageSize)),
+		mcp.WithNumber("page", mcp.Description(params.PageDesc), mcp.DefaultNumber(1)),
+		mcp.WithNumber("per_page", mcp.Description(params.PaginationDesc), mcp.DefaultNumber(30)),
 	)
 )
 
-// init registers all MCP tools in Tool at package initialization.
-// This function ensures the handler functions are registered before server usage.
 func init() {
-	registerTools()
+	Tool.RegisterRead(server.ServerTool{Tool: GetMyUserInfoTool, Handler: GetUserInfoFn})
+	Tool.RegisterRead(server.ServerTool{Tool: GetUserOrgsTool, Handler: GetUserOrgsFn})
 }
 
-// registerTools registers all local MCP tool definitions and their handler functions.
-// To add new functionality, append your tool/handler pair to the tools slice below.
-func registerTools() {
-	tools := []server.ServerTool{
-		{Tool: GetMyUserInfoTool, Handler: GetUserInfoFn},
-		{Tool: GetUserOrgsTool, Handler: GetUserOrgsFn},
-	}
-	for _, t := range tools {
-		Tool.RegisterRead(t)
-	}
-}
-
-// GetUserInfoFn is the handler for "get_me" MCP tool requests.
-// Logs invocation, fetches current user info from gitea, wraps result for MCP.
 func GetUserInfoFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("[User] Called GetUserInfoFn")
 	client, err := gitea.ClientFromContext(ctx)
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("get gitea client err: %v", err))
@@ -81,15 +53,11 @@ func GetUserInfoFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolR
 	if err != nil {
 		return to.ErrorResult(fmt.Errorf("get user info err: %v", err))
 	}
-	return to.TextResult(slimUserDetail(user))
+	return to.TextResult(slim.UserDetail(user))
 }
 
-// GetUserOrgsFn is the handler for "get_user_orgs" MCP tool requests.
-// Logs invocation, pulls validated pagination arguments from request,
-// performs Gitea organization listing, and wraps the result for MCP.
 func GetUserOrgsFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
-	log.Debugf("[User] Called GetUserOrgsFn")
-	page, pageSize := params.GetPagination(req.GetArguments(), defaultPageSize)
+	page, pageSize := params.GetPagination(req.GetArguments(), 30)
 
 	opt := gitea_sdk.ListOrgsOptions{
 		ListOptions: gitea_sdk.ListOptions{