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

nginx/nginx.conf

@@ -8,26 +8,20 @@ http {
     sendfile      on;
     keepalive_timeout 65;
 
-    # Use Docker's internal DNS so upstream IPs re-resolve after container restarts
+    # Use Docker's internal DNS; valid=10s forces re-resolution after container restarts.
+    # Variables in proxy_pass activate this resolver (upstream blocks do not).
     resolver 127.0.0.11 valid=10s ipv6=off;
 
-    upstream api {
-        server api:8000;
-    }
-
-    upstream frontend {
-        server frontend:3000;
-    }
-
     server {
         listen 80;
         server_name _;
 
         client_max_body_size 10M;
 
-        # API
+        # API — variable forces re-resolution via resolver on each request cycle
         location /api/ {
-            proxy_pass http://api;
+            set $api http://api:8000;
+            proxy_pass $api;
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
@@ -38,14 +32,16 @@ http {
 
         # Next.js static assets (long cache)
         location /_next/static/ {
-            proxy_pass http://frontend;
+            set $frontend http://frontend:3000;
+            proxy_pass $frontend;
             proxy_cache_valid 200 1d;
             add_header Cache-Control "public, max-age=86400, immutable";
         }
 
         # Everything else → frontend
         location / {
-            proxy_pass http://frontend;
+            set $frontend http://frontend:3000;
+            proxy_pass $frontend;
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;