docs: document development workflow and MCP tool usage

- Add CLAUDE.md file with guidance for using Claude Code in this repository
- Document development commands, architecture overview, and tool organization
- List available MCP tools with their main categories and functions
- Provide notes on configuration, authentication, and common development practices

Signed-off-by: appleboy <appleboy.tw@gmail.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Commands
+
+**Build**: `make build` - Build the gitea-mcp binary
+**Install**: `make install` - Build and install to GOPATH/bin
+**Clean**: `make clean` - Remove build artifacts
+**Test**: `go test ./...` - Run all tests
+**Hot reload**: `make dev` - Start development server with hot reload (requires air)
+**Dependencies**: `make vendor` - Tidy and verify module dependencies
+
+## Architecture Overview
+
+This is a **Gitea MCP (Model Context Protocol) Server** written in Go that provides MCP tools for interacting with Gitea repositories, issues, pull requests, users, and more.
+
+**Core Components**:
+
+- `main.go` + `cmd/cmd.go`: CLI entry point and flag parsing
+- `operation/operation.go`: Main server setup and tool registration
+- `pkg/tool/tool.go`: Tool registry with read/write categorization
+- `operation/*/`: Individual tool modules (user, repo, issue, pull, search, wiki, etc.)
+
+**Transport Modes**:
+
+- **stdio** (default): Standard input/output for MCP clients
+- **http**: HTTP server mode on configurable port (default 8080)
+
+**Authentication**:
+
+- Global token via `--token` flag or `GITEA_ACCESS_TOKEN` env var
+- HTTP mode supports per-request Bearer token override in Authorization header
+- Token precedence: HTTP Authorization header > CLI flag > environment variable
+
+**Tool Organization**:
+
+- Tools are categorized as read-only or write operations
+- `--read-only` flag exposes only read tools
+- Tool modules register via `Tool.RegisterRead()` and `Tool.RegisterWrite()`
+
+**Key Configuration**:
+
+- Default Gitea host: `https://gitea.com` (override with `--host` or `GITEA_HOST`)
+- Environment variables can override CLI flags: `MCP_MODE`, `GITEA_READONLY`, `GITEA_DEBUG`, `GITEA_INSECURE`
+- Logs are written to `~/.gitea-mcp/gitea-mcp.log` with rotation
+
+## Available Tools
+
+The server provides 40+ MCP tools covering:
+
+- **User**: get_my_user_info, get_user_orgs, search_users
+- **Repository**: create_repo, fork_repo, list_my_repos, search_repos
+- **Branches/Tags**: create_branch, delete_branch, list_branches, create_tag, list_tags
+- **Files**: get_file_content, create_file, update_file, delete_file, get_dir_content
+- **Issues**: create_issue, list_repo_issues, create_issue_comment, edit_issue
+- **Pull Requests**: create_pull_request, list_repo_pull_requests, get_pull_request_by_index
+- **Releases**: create_release, list_releases, get_latest_release
+- **Wiki**: create_wiki_page, update_wiki_page, list_wiki_pages
+- **Search**: search_repos, search_users, search_org_teams
+- **Version**: get_gitea_mcp_server_version
+
+## Common Development Patterns
+
+**Testing**: Use `go test ./operation -run TestFunctionName` for specific tests
+
+**Token Context**: HTTP requests use `pkg/context.TokenContextKey` for request-scoped token access
+
+**Flag Access**: All packages access configuration via global variables in `pkg/flag/flag.go`
+
+**Graceful Shutdown**: HTTP mode implements graceful shutdown with 10-second timeout on SIGTERM/SIGINT