Add BranchExists/CreateBranch/UpsertFile gitea client methods and the
file_write_branch MCP tool. Branch is auto-created from base (or repo
default_branch) when it doesn't exist; file is upserted via PUT contents.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Adds GetFileContents to the gitea client and a file_read MCP tool.
When ref is omitted, the tool resolves the repo default_branch via
GetRepo before fetching contents. Decoded content capped at 1 MiB.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
