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/api/follows.py

@@ -7,11 +7,12 @@ from app.core.dependencies import get_current_user
 from app.database import get_db
 from app.models import Follow
 from app.models.user import User
-from app.schemas.schemas import FollowCreate, FollowSchema
+from app.schemas.schemas import FollowCreate, FollowModeUpdate, FollowSchema
 
 router = APIRouter()
 
 VALID_FOLLOW_TYPES = {"bill", "member", "topic"}
+VALID_MODES = {"neutral", "pocket_veto", "pocket_boost"}
 
 
 @router.get("", response_model=list[FollowSchema])
@@ -58,6 +59,26 @@ async def add_follow(
     return follow
 
 
+@router.patch("/{follow_id}/mode", response_model=FollowSchema)
+async def update_follow_mode(
+    follow_id: int,
+    body: FollowModeUpdate,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    if body.follow_mode not in VALID_MODES:
+        raise HTTPException(status_code=400, detail=f"follow_mode must be one of {VALID_MODES}")
+    follow = await db.get(Follow, follow_id)
+    if not follow:
+        raise HTTPException(status_code=404, detail="Follow not found")
+    if follow.user_id != current_user.id:
+        raise HTTPException(status_code=403, detail="Not your follow")
+    follow.follow_mode = body.follow_mode
+    await db.commit()
+    await db.refresh(follow)
+    return follow
+
+
 @router.delete("/{follow_id}", status_code=204)
 async def remove_follow(
     follow_id: int,