feat: align claim/lock gates with branches-only worktrees (#275)

Allow issue lock from base-equivalent branches/ worktrees instead of
requiring the literal master/main branch name. Runtime preflight and
mark_issue/lock_issue now inspect the declared active task workspace so
dirty control-checkout state does not block clean task worktrees.

Closes #275

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

task_capability_map.py

@@ -28,6 +28,10 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.issue.comment",
         "role": "author",
     },
+    "lock_issue": {
+        "permission": "gitea.issue.comment",
+        "role": "author",
+    },
     "set_issue_labels": {
         "permission": "gitea.issue.comment",
         "role": "author",
@@ -110,4 +114,4 @@ def required_role(task: str) -> str:
 
 def tool_required_permission(tool_name: str) -> str:
     """Return the operation an issue-mutating tool must gate on."""
-    return required_permission(ISSUE_MUTATION_TOOL_TASKS[tool_name])
+    return required_permission(ISSUE_MUTATION_TOOL_TASKS[tool_name])