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/repo/slim_test.go

@@ -0,0 +1,142 @@
+package repo
+
+import (
+	"testing"
+
+	gitea_sdk "code.gitea.io/sdk/gitea"
+)
+
+func TestSlimRepo(t *testing.T) {
+	r := &gitea_sdk.Repository{
+		ID:            1,
+		FullName:      "org/repo",
+		Description:   "A test repo",
+		HTMLURL:       "https://gitea.com/org/repo",
+		CloneURL:      "https://gitea.com/org/repo.git",
+		SSHURL:        "git@gitea.com:org/repo.git",
+		DefaultBranch: "main",
+		Private:       false,
+		Fork:          false,
+		Archived:      false,
+		Language:      "Go",
+		Stars:         10,
+		Forks:         2,
+		Owner:         &gitea_sdk.User{UserName: "org"},
+		Topics:        []string{"mcp", "gitea"},
+	}
+
+	m := slimRepo(r)
+
+	if m["full_name"] != "org/repo" {
+		t.Errorf("expected full_name org/repo, got %v", m["full_name"])
+	}
+	if m["owner"] != "org" {
+		t.Errorf("expected owner org, got %v", m["owner"])
+	}
+	topics := m["topics"].([]string)
+	if len(topics) != 2 {
+		t.Errorf("expected 2 topics, got %d", len(topics))
+	}
+}
+
+func TestSlimTag(t *testing.T) {
+	tag := &gitea_sdk.Tag{
+		Name:    "v1.0.0",
+		Message: "Release v1.0.0",
+		Commit:  &gitea_sdk.CommitMeta{SHA: "abc123"},
+	}
+
+	m := slimTag(tag)
+	if m["name"] != "v1.0.0" {
+		t.Errorf("expected name v1.0.0, got %v", m["name"])
+	}
+	if m["message"] != "Release v1.0.0" {
+		t.Errorf("expected message, got %v", m["message"])
+	}
+
+	// List variant omits message
+	list := slimTags([]*gitea_sdk.Tag{tag})
+	if _, ok := list[0]["message"]; ok {
+		t.Error("Tags list should omit message")
+	}
+	if list[0]["name"] != "v1.0.0" {
+		t.Errorf("expected name in list, got %v", list[0]["name"])
+	}
+}
+
+func TestSlimRelease(t *testing.T) {
+	r := &gitea_sdk.Release{
+		ID:        1,
+		TagName:   "v1.0.0",
+		Title:     "First Release",
+		Note:      "Release notes",
+		IsDraft:   false,
+		Publisher: &gitea_sdk.User{UserName: "alice"},
+	}
+
+	m := slimRelease(r)
+	if m["tag_name"] != "v1.0.0" {
+		t.Errorf("expected tag_name v1.0.0, got %v", m["tag_name"])
+	}
+	if m["body"] != "Release notes" {
+		t.Errorf("expected body from Note field, got %v", m["body"])
+	}
+	if m["author"] != "alice" {
+		t.Errorf("expected author alice, got %v", m["author"])
+	}
+}
+
+func TestSlimContents(t *testing.T) {
+	content := "package main"
+	encoding := "base64"
+	htmlURL := "https://gitea.com/org/repo/src/branch/main/main.go"
+	c := &gitea_sdk.ContentsResponse{
+		Name:     "main.go",
+		Path:     "main.go",
+		SHA:      "abc123",
+		Type:     "file",
+		Size:     12,
+		Content:  &content,
+		Encoding: &encoding,
+		HTMLURL:  &htmlURL,
+	}
+
+	m := slimContents(c)
+	if m["name"] != "main.go" {
+		t.Errorf("expected name main.go, got %v", m["name"])
+	}
+	if m["content"] != "package main" {
+		t.Errorf("expected content, got %v", m["content"])
+	}
+}
+
+func TestSlimDirEntries(t *testing.T) {
+	entries := []*gitea_sdk.ContentsResponse{
+		{Name: "src", Path: "src", Type: "dir", Size: 0},
+		{Name: "main.go", Path: "main.go", Type: "file", Size: 100},
+	}
+
+	result := slimDirEntries(entries)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 entries, got %d", len(result))
+	}
+	if result[0]["name"] != "src" {
+		t.Errorf("expected first entry name src, got %v", result[0]["name"])
+	}
+	// Dir entries should not have content
+	if _, ok := result[0]["content"]; ok {
+		t.Error("dir entries should not have content field")
+	}
+}
+
+func TestSlimTags_Nil(t *testing.T) {
+	if r := slimTags(nil); len(r) != 0 {
+		t.Errorf("expected empty slice, got %v", r)
+	}
+}
+
+func TestSlimReleases_Nil(t *testing.T) {
+	if r := slimReleases(nil); len(r) != 0 {
+		t.Errorf("expected empty slice, got %v", r)
+	}
+}