Slice 5: Gitea forge - PRs and Merge & clean up

New internal/forge (provider-abstracted, Gitea impl via code.gitea.io/sdk/gitea) with tested remote-URL parsing and read+write ops: list open PRs, and merge-and-cleanup (squash-merge + delete head branch when head/base share a repo). Service resolves repo->owner/repo from remotes (prefers origin) and records a pr-merged event; config gains GITEA_URL/GITEA_TOKEN (forge disabled without both). MCP tools list_prs and merge_and_cleanup_pr (merge tool tells Claude to confirm first, 1.4). HTTP GET /api/repo/prs, POST /api/repo/pr/merge. New <pr-list> component with a confirming Merge & clean up button, hidden when no forge. Verified graceful-disabled path; real merge pending token + a designated PR.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/templates/help.html

@@ -62,6 +62,18 @@
       project and this activity, so you stay on the same page.
     </p>
 
+    <h2>Pull requests: Merge &amp; clean up</h2>
+    <p>
+      When a repository is hosted on your Gitea server, its open pull requests
+      appear under the details panel. Each has a <strong>Merge &amp; clean up</strong>
+      button: it squash-merges the pull request and <strong>deletes its
+      branch</strong> in one step, so finished work doesn't leave branches lying
+      around. You'll be asked to confirm — it names the pull request and the branch
+      that will be deleted — because it can't be undone (the merged history stays
+      on the server; only the branch is removed). If you don't use a Gitea server,
+      this section stays hidden.
+    </p>
+
     <h2>Handing a project off to Claude</h2>
     <p>
       When GitManager is connected to Claude, you can hand the current project