Adds plugins/gitea/skills/gitea-branches/ per ADR 0011, covering
list_branches/create_branch/delete_branch (migrated from the flat
plugins/bin/skills/gitea/ dispatch) plus list_commits/get_commit (new
read-only commit-history domain). Call signatures were re-verified live
via ToolSearch against the deployed gitea-mcp server rather than copied
from api-reference.md, per issue #6 comment #849's root-cause fix.
Bumps the gitea plugin to 1.1.0 in both manifests for the new skill.