feat(notifications): follow modes, milestone alerts, notification enhancements

Follow Modes (neutral / pocket_veto / pocket_boost):
- Alembic migration 0013 adds follow_mode column to follows table
- FollowButton rewritten as mode-aware dropdown for bills; simple toggle for members/topics
- PATCH /api/follows/{id}/mode endpoint with validation
- Dispatcher filters pocket_veto follows (suppress new_document/new_amendment events)
- Dispatcher adds ntfy Actions header for pocket_boost follows

Change-driven (milestone) Alerts:
- New notification_utils.py with shared emit helpers and 30-min dedup
- congress_poller emits bill_updated events on milestone action text
- llm_processor replaced with shared emit util (also notifies member/topic followers)

Notification Enhancements:
- ntfy priority levels (high for bill_updated, default for others)
- Quiet hours (UTC): dispatcher holds events outside allowed window
- Digest mode (daily/weekly): send_notification_digest Celery beat task
- Notification history endpoint + Recent Alerts UI section
- Enriched following page (bill titles, member photos/details via sub-components)
- Follow mode test buttons in admin settings panel

Infrastructure:
- nginx: switch upstream blocks to set $variable proxy_pass so Docker DNS
  re-resolves upstream IPs after container rebuilds (valid=10s)
- TROUBLESHOOTING.md documenting common Docker/nginx/postgres gotchas

Authored-By: Jack Levy

backend/app/workers/notification_utils.py

@@ -0,0 +1,137 @@
+"""
+Shared notification utilities — used by llm_processor, congress_poller, etc.
+Centralised here to avoid circular imports.
+"""
+from datetime import datetime, timedelta, timezone
+
+_MILESTONE_KEYWORDS = [
+    "passed", "failed", "agreed to",
+    "signed", "vetoed", "enacted",
+    "presented to the president",
+    "ordered to be reported", "ordered reported",
+    "reported by", "discharged",
+    "placed on",   # placed on calendar
+    "cloture", "roll call",
+]
+
+# Events created within this window for the same (user, bill, event_type) are suppressed
+_DEDUP_MINUTES = 30
+
+
+def is_milestone_action(action_text: str) -> bool:
+    t = (action_text or "").lower()
+    return any(kw in t for kw in _MILESTONE_KEYWORDS)
+
+
+def _build_payload(bill, action_summary: str) -> dict:
+    from app.config import settings
+    base_url = (settings.PUBLIC_URL or settings.LOCAL_URL).rstrip("/")
+    return {
+        "bill_title": bill.short_title or bill.title or "",
+        "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}",
+    }
+
+
+def _is_duplicate(db, user_id: int, bill_id: str, event_type: str) -> bool:
+    """True if an identical event was already created within the dedup window."""
+    from app.models.notification import NotificationEvent
+    cutoff = datetime.now(timezone.utc) - timedelta(minutes=_DEDUP_MINUTES)
+    return db.query(NotificationEvent).filter_by(
+        user_id=user_id,
+        bill_id=bill_id,
+        event_type=event_type,
+    ).filter(NotificationEvent.created_at > cutoff).first() is not None
+
+
+def emit_bill_notification(db, bill, event_type: str, action_summary: str) -> int:
+    """Create NotificationEvent rows for every user following this bill. Returns count."""
+    from app.models.follow import Follow
+    from app.models.notification import NotificationEvent
+
+    followers = db.query(Follow).filter_by(follow_type="bill", follow_value=bill.bill_id).all()
+    if not followers:
+        return 0
+
+    payload = _build_payload(bill, action_summary)
+    count = 0
+    for follow in followers:
+        if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):
+            continue
+        db.add(NotificationEvent(
+            user_id=follow.user_id,
+            bill_id=bill.bill_id,
+            event_type=event_type,
+            payload=payload,
+        ))
+        count += 1
+    if count:
+        db.commit()
+    return count
+
+
+def emit_member_follow_notifications(db, bill, event_type: str, action_summary: str) -> int:
+    """Notify users following the bill's sponsor (dedup prevents double-alerts for bill+member followers)."""
+    if not bill.sponsor_id:
+        return 0
+
+    from app.models.follow import Follow
+    from app.models.notification import NotificationEvent
+
+    followers = db.query(Follow).filter_by(follow_type="member", follow_value=bill.sponsor_id).all()
+    if not followers:
+        return 0
+
+    payload = _build_payload(bill, action_summary)
+    count = 0
+    for follow in followers:
+        if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):
+            continue
+        db.add(NotificationEvent(
+            user_id=follow.user_id,
+            bill_id=bill.bill_id,
+            event_type=event_type,
+            payload=payload,
+        ))
+        count += 1
+    if count:
+        db.commit()
+    return count
+
+
+def emit_topic_follow_notifications(db, bill, event_type: str, action_summary: str, topic_tags: list) -> int:
+    """Notify users following any of the bill's topic tags."""
+    if not topic_tags:
+        return 0
+
+    from app.models.follow import Follow
+    from app.models.notification import NotificationEvent
+
+    # Collect unique followers across all matching tags
+    seen_user_ids: set[int] = set()
+    followers = []
+    for tag in topic_tags:
+        for follow in db.query(Follow).filter_by(follow_type="topic", follow_value=tag).all():
+            if follow.user_id not in seen_user_ids:
+                seen_user_ids.add(follow.user_id)
+                followers.append(follow)
+
+    if not followers:
+        return 0
+
+    payload = _build_payload(bill, action_summary)
+    count = 0
+    for follow in followers:
+        if _is_duplicate(db, follow.user_id, bill.bill_id, event_type):
+            continue
+        db.add(NotificationEvent(
+            user_id=follow.user_id,
+            bill_id=bill.bill_id,
+            event_type=event_type,
+            payload=payload,
+        ))
+        count += 1
+    if count:
+        db.commit()
+    return count