fix(auth): route delete_branch capability to the reconciler role (Closes #729)

Remote post-merge branch deletion was blocked because the capability
resolver classified delete_branch as an author-role task while
gitea.branch.delete is granted only to prgs-reconciler. No configured
profile could satisfy both the permission gate and the role gate, so
every deletion failed closed with performed=false.

Re-home delete_branch from the author role to the reconciler role in
both single-source-of-truth maps:
  - task_capability_map.TASK_CAPABILITY_MAP["delete_branch"].role
  - role_session_router: TASK_REQUIRED_ROLE + AUTHOR_TASKS/RECONCILER_TASKS

resolve_task_capability("delete_branch") now resolves to prgs-reconciler.
In gitea_delete_branch, the reconciler is now the delete-capable role and
performs raw deletion through the existing reconciliation-cleanup-phase
authorization gate (operator approval + safe_to_delete proof) plus the
preservation/protected guards; the prior reconciler->cleanup redirect is
removed as it would orphan that guarded flow. Author, reviewer, and
merger stay denied by the permission gate and the required-role gate.
gitea_cleanup_merged_pr_branch remains a separate reconciler-owned path
with independent merged/ancestry/ownership verification.

Tests: reconciler resolves + performs eligible deletion; author/reviewer/
merger denied even when holding the permission; protected/preservation
branches remain fail-closed; both role maps asserted in agreement.
Updated pre-existing tests that encoded the superseded author-delete /
#687 reconciler-redirect contract. Full suite: 3190 passed, 6 skipped,
1 pre-existing unrelated failure (test_issue_702 create_pr stale-binding).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01UracxyRHQw49rZBaexHdft

tests/test_mcp_server.py

@@ -1471,8 +1471,9 @@ class TestReviewPR(unittest.TestCase):
 class TestDeleteBranch(unittest.TestCase):
 
     DELETE_PROFILE = {
-        "profile_name": "test-author-deleter",
-        "role": "author",
+        # #729: delete_branch is reconciler-owned.
+        "profile_name": "test-reconciler-deleter",
+        "role": "reconciler",
         "allowed_operations": [
             "gitea.read",
             "gitea.pr.create",
@@ -1488,7 +1489,7 @@ class TestDeleteBranch(unittest.TestCase):
     @patch("mcp_server.get_auth_header", return_value=FAKE_AUTH)
     def test_delete_branch(self, _auth, mock_api, _profile):
         mcp_server.record_preflight_check("whoami")
-        mcp_server.record_preflight_check("capability", resolved_role="author")
+        mcp_server.record_preflight_check("capability", resolved_role="reconciler")
         mock_api.return_value = {}
         result = gitea_delete_branch(branch="feat/branch")
         self.assertTrue(result["success"])