feat(phase2): fact/inference labeling, change-driven alerts, admin cleanup

- Add label: cited_fact | inference to LLM brief schema (all 4 providers)
- Inferred badge in AIBriefCard for inference-labeled points
- backfill_brief_labels Celery task: classifies existing cited points in-place
- POST /api/admin/backfill-labels + unlabeled_briefs stat counter
- Expand milestone keywords: markup, conference
- Add is_referral_action() for committee referrals (referred to)
- Two-tier milestone notifications: progress tier (all follow modes) and
  referral tier (pocket_veto/boost only, neutral suppressed)
- Topic followers now receive bill_updated milestone notifications via
  latest brief topic_tags lookup in _update_bill_if_changed()
- Admin Manual Controls: collapsible Maintenance section for backfill tasks
- Update ARCHITECTURE.md and roadmap for Phase 2 completion

Co-Authored-By: Jack Levy

backend/app/workers/notification_utils.py

@@ -10,8 +10,15 @@ _MILESTONE_KEYWORDS = [
     "presented to the president",
     "ordered to be reported", "ordered reported",
     "reported by", "discharged",
-    "placed on",   # placed on calendar
+    "placed on",        # placed on calendar
     "cloture", "roll call",
+    "markup",           # markup session scheduled/completed
+    "conference",       # conference committee activity
+]
+
+# Committee referral — meaningful for pocket_veto/boost but noisy for neutral
+_REFERRAL_KEYWORDS = [
+    "referred to",
 ]
 
 # Events created within this window for the same (user, bill, event_type) are suppressed
@@ -23,7 +30,12 @@ def is_milestone_action(action_text: str) -> bool:
     return any(kw in t for kw in _MILESTONE_KEYWORDS)
 
 
-def _build_payload(bill, action_summary: str) -> dict:
+def is_referral_action(action_text: str) -> bool:
+    t = (action_text or "").lower()
+    return any(kw in t for kw in _REFERRAL_KEYWORDS)
+
+
+def _build_payload(bill, action_summary: str, milestone_tier: str = "progress") -> dict:
     from app.config import settings
     base_url = (settings.PUBLIC_URL or settings.LOCAL_URL).rstrip("/")
     return {
@@ -31,6 +43,7 @@ def _build_payload(bill, action_summary: str) -> dict:
         "bill_label": f"{bill.bill_type.upper()} {bill.bill_number}",
         "brief_summary": (action_summary or "")[:300],
         "bill_url": f"{base_url}/bills/{bill.bill_id}",
+        "milestone_tier": milestone_tier,
     }
 
 
@@ -45,7 +58,9 @@ def _is_duplicate(db, user_id: int, bill_id: str, event_type: str) -> bool:
     ).filter(NotificationEvent.created_at > cutoff).first() is not None
 
 
-def emit_bill_notification(db, bill, event_type: str, action_summary: str) -> int:
+def emit_bill_notification(
+    db, bill, event_type: str, action_summary: str, milestone_tier: str = "progress"
+) -> int:
     """Create NotificationEvent rows for every user following this bill. Returns count."""
     from app.models.follow import Follow
     from app.models.notification import NotificationEvent
@@ -54,7 +69,7 @@ def emit_bill_notification(db, bill, event_type: str, action_summary: str) -> in
     if not followers:
         return 0
 
-    payload = _build_payload(bill, action_summary)
+    payload = _build_payload(bill, action_summary, milestone_tier)
     count = 0
     for follow in followers:
         if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):
@@ -71,7 +86,9 @@ def emit_bill_notification(db, bill, event_type: str, action_summary: str) -> in
     return count
 
 
-def emit_member_follow_notifications(db, bill, event_type: str, action_summary: str) -> int:
+def emit_member_follow_notifications(
+    db, bill, event_type: str, action_summary: str, milestone_tier: str = "progress"
+) -> int:
     """Notify users following the bill's sponsor (dedup prevents double-alerts for bill+member followers)."""
     if not bill.sponsor_id:
         return 0
@@ -83,7 +100,7 @@ def emit_member_follow_notifications(db, bill, event_type: str, action_summary:
     if not followers:
         return 0
 
-    payload = _build_payload(bill, action_summary)
+    payload = _build_payload(bill, action_summary, milestone_tier)
     count = 0
     for follow in followers:
         if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):
@@ -100,7 +117,10 @@ def emit_member_follow_notifications(db, bill, event_type: str, action_summary:
     return count
 
 
-def emit_topic_follow_notifications(db, bill, event_type: str, action_summary: str, topic_tags: list) -> int:
+def emit_topic_follow_notifications(
+    db, bill, event_type: str, action_summary: str, topic_tags: list,
+    milestone_tier: str = "progress",
+) -> int:
     """Notify users following any of the bill's topic tags."""
     if not topic_tags:
         return 0
@@ -120,7 +140,7 @@ def emit_topic_follow_notifications(db, bill, event_type: str, action_summary: s
     if not followers:
         return 0
 
-    payload = _build_payload(bill, action_summary)
+    payload = _build_payload(bill, action_summary, milestone_tier)
     count = 0
     for follow in followers:
         if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):