fix: authoritative cross-role generic queue allocation (Closes #840)

Add controller-owned cross_role allocation mode that inspects the full
queue and returns one selection with required role/profile/action and
lease evidence. Document process_work_queue routing, normalize
controller role metadata, and keep the dashboard explanatory only.

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

task_capability_map.py

@@ -309,8 +309,10 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.pr.create",
         "role": "author",
     },
-    # #600: controller-owned allocator — any authenticated profile may call;
-    # routing enforces role match to selected work. Uses control-plane DB (#613).
+    # #600: workers and controller may call with gitea.read; role-scoped workers
+    # pass role=author|reviewer|merger|reconciler. Cross-role routing is the
+    # controller default (#840). The canonical generic queue *task type* is
+    # process_work_queue (controller-only below).
     "allocate_next_work": {
         "permission": "gitea.read",
         "role": "author",
@@ -319,6 +321,19 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
         "permission": "gitea.read",
         "role": "author",
     },
+    # #840: documented generic queue task — controller routes only.
+    "process_work_queue": {
+        "permission": "gitea.read",
+        "role": "controller",
+    },
+    "process-work-queue": {
+        "permission": "gitea.read",
+        "role": "controller",
+    },
+    "cross_role_allocate": {
+        "permission": "gitea.read",
+        "role": "controller",
+    },
 
     # #601 first-class lease lifecycle — inspect/list need read; mutations gate on
     # ownership in the control-plane DB (not a separate Gitea write permission).