Closes#106.
Adds 12 new MCP tools (list/get/download/create/edit/delete × issue +
comment) backed by a new pkg/forgejo/rawhttp.go helper. Download tools
return inline BlobResourceContents under 1 MiB and metadata +
browser_download_url at or above the cap, per the design agreed with
@heathen711 on issue #106.
Includes unit tests, demos, and an e2e script under test/e2e/.
cf7d392086