feat: slim tool responses (#141)

Reduce token usage by slimming tool responses. Instead of returning full Gitea SDK objects (with nested user/repo objects, avatars, permissions, etc.), each operation now has a colocated `slim.go` that extracts only the fields an LLM needs. List endpoints return even fewer fields than single-item endpoints.

Other changes:
- Add `params` helpers to DRY parameter extraction across 40+ handlers
- Remove `{"Result": ...}` wrapper for flatter responses
- Reduce default pageSize from 100 to 30

Fixes: https://gitea.com/gitea/gitea-mcp/issues/128

*Created by Claude on behalf of @silverwind*

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/141
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/to/to.go

@@ -8,13 +8,8 @@ import (
 	"github.com/mark3labs/mcp-go/mcp"
 )
 
-type textResult struct {
-	Result any
-}
-
 func TextResult(v any) (*mcp.CallToolResult, error) {
-	result := textResult{v}
-	resultBytes, err := json.Marshal(result)
+	resultBytes, err := json.Marshal(v)
 	if err != nil {
 		return nil, fmt.Errorf("marshal result err: %v", err)
 	}