feat(gitea): add gitea-branches skill (branches + commits)

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.

plugins/gitea/skills/gitea-branches/references/sources.md

@@ -0,0 +1,25 @@
+# Sources
+
+**Note on call signatures:** per `docs/adr/0011-gitea-skill-deep-modules.md`, the tool parameter
+signatures in `references/branches.md` and `references/commits.md` were re-verified live via
+`ToolSearch` against the deployed `gitea-mcp` server at authoring time — they are not copied
+verbatim from `api-reference.md` below. This resolves issue #6 comment #849's root-cause finding
+that a prior skill was authored from API docs that had drifted from the actual MCP tool schema.
+The research docs cited here informed gotchas, response shapes, and workflow context, not the
+parameter lists themselves.
+
+## gitea-mcp-repo
+
+- **URL:** https://gitea.com/gitea/gitea-mcp
+- **Description:** Official gitea-mcp repository (v1.3.0); operation/*.go source files documenting all 55 MCP tools, their parameters, and CLI flags. Informed the dispatch table and pagination / 404-may-mean-403 gotchas in SKILL.md, and the list/create/delete branch and list/get commit mechanics (including 409 conflict and default-branch fallback behavior) in references/branches.md and references/commits.md.
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+- **Contributing files:** SKILL.md, references/branches.md, references/commits.md
+- **Status:** `extracted`
+
+## gitea-mcp-slim-go
+
+- **URL:** https://gitea.com/gitea/gitea-mcp/raw/branch/main/operation/repo/slim.go
+- **Description:** Slim response shape structs from gitea-mcp source; defines exactly which fields the MCP server returns for branches (name, protected, commit_sha) and commits (sha, html_url, created, message, author), and informed get_commit's always-populated guarantee vs. list_commits' conditional fields.
+- **Research doc:** plugins/gitea/docs/research/docs/gitea/sources.md
+- **Contributing files:** references/branches.md, references/commits.md
+- **Status:** `extracted`