feat: dual-mode — MCP server and CLI skill in one file

Expose the same 66 Gitea tools two ways from server/gitea_mcp.py:
- MCP server (no subcommand -> mcp.run()), as before
- CLI: `<tool> --flags` prints one JSON object {success, data/error}

A new @tool decorator registers each function in both FastMCP and a TOOLS
registry; a CLI dispatcher builds argparse from each function's signature and
wraps results in the repo's JSON+success contract. Adds `list-tools` for
discovery. No tool logic duplicated.

- Rewrite skills/gitea/SKILL.md for CLI-first usage (MCP kept as an option)
- Sync version to 0.3.0 across plugin.json, pyproject.toml, SKILL.md
- Add tests/unit/test_cli.py (dispatch routing, flag typing, errors, main)
- Document dual-mode in README.md and CLAUDE.md
- Ignore coverage artifacts

Tests: 119 passed, 93% coverage.

pyproject.toml

@@ -1,7 +1,7 @@
 [project]
 name = "gitea-platform-mcp"
-version = "0.2.0"
-description = "Full Gitea platform management via MCP"
+version = "0.3.0"
+description = "Full Gitea platform management — MCP server and CLI skill in one file"
 requires-python = ">=3.10"
 dependencies = [
     "mcp[cli]>=1.0",