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>

operation/timetracking/slim.go

@@ -0,0 +1,47 @@
+package timetracking
+
+import (
+	gitea_sdk "code.gitea.io/sdk/gitea"
+)
+
+func slimStopWatch(s *gitea_sdk.StopWatch) map[string]any {
+	if s == nil {
+		return nil
+	}
+	return map[string]any{
+		"issue_index": s.IssueIndex,
+		"issue_title": s.IssueTitle,
+		"repo_name":   s.RepoName,
+		"repo_owner":  s.RepoOwnerName,
+		"created":     s.Created,
+		"seconds":     s.Seconds,
+	}
+}
+
+func slimStopWatches(watches []*gitea_sdk.StopWatch) []map[string]any {
+	out := make([]map[string]any, 0, len(watches))
+	for _, s := range watches {
+		out = append(out, slimStopWatch(s))
+	}
+	return out
+}
+
+func slimTrackedTime(t *gitea_sdk.TrackedTime) map[string]any {
+	if t == nil {
+		return nil
+	}
+	return map[string]any{
+		"id":        t.ID,
+		"time":      t.Time,
+		"user_name": t.UserName,
+		"created":   t.Created,
+	}
+}
+
+func slimTrackedTimes(times []*gitea_sdk.TrackedTime) []map[string]any {
+	out := make([]map[string]any, 0, len(times))
+	for _, t := range times {
+		out = append(out, slimTrackedTime(t))
+	}
+	return out
+}