feat: per-user notifications (ntfy + RSS), deduplicated actions, backfill task

Notifications:
- New /notifications page accessible to all users (ntfy + RSS config)
- ntfy now supports no-auth, Bearer token, and HTTP Basic auth (for ACL-protected self-hosted servers)
- RSS enabled/disabled independently of ntfy; token auto-generated on first GET
- Notification settings removed from admin-only Settings page; replaced with link card
- Sidebar adds Notifications nav link for all users
- notification_dispatcher.py: fan-out now marks RSS events dispatched independently

Action history:
- Migration 0012: deduplicates existing bill_actions rows and adds UNIQUE(bill_id, action_date, action_text)
- congress_poller.py: replaces existence-check inserts with ON CONFLICT DO NOTHING (race-condition safe)
- Added backfill_all_bill_actions task (no date filter) + admin endpoint POST /backfill-all-actions

Authored-By: Jack Levy

backend/app/services/congress_api.py

@@ -15,6 +15,30 @@ from app.config import settings
 
 BASE_URL = "https://api.congress.gov/v3"
 
+_BILL_TYPE_SLUG = {
+    "hr": "house-bill",
+    "s": "senate-bill",
+    "hjres": "house-joint-resolution",
+    "sjres": "senate-joint-resolution",
+    "hres": "house-resolution",
+    "sres": "senate-resolution",
+    "hconres": "house-concurrent-resolution",
+    "sconres": "senate-concurrent-resolution",
+}
+
+
+def _congress_ordinal(n: int) -> str:
+    if 11 <= n % 100 <= 13:
+        return f"{n}th"
+    suffixes = {1: "st", 2: "nd", 3: "rd"}
+    return f"{n}{suffixes.get(n % 10, 'th')}"
+
+
+def build_bill_public_url(congress: int, bill_type: str, bill_number: int) -> str:
+    """Return the public congress.gov page URL for a bill (not the API endpoint)."""
+    slug = _BILL_TYPE_SLUG.get(bill_type.lower(), bill_type.lower())
+    return f"https://www.congress.gov/bill/{_congress_ordinal(congress)}-congress/{slug}/{bill_number}"
+
 
 def _get_current_congress() -> int:
     """Calculate the current Congress number. 119th started Jan 3, 2025."""
@@ -98,7 +122,7 @@ def parse_bill_from_api(data: dict, congress: int) -> dict:
         "latest_action_text": latest_action.get("text"),
         "status": latest_action.get("text", "")[:100] if latest_action.get("text") else None,
         "chamber": "House" if bill_type.startswith("h") else "Senate",
-        "congress_url": data.get("url"),
+        "congress_url": build_bill_public_url(congress, bill_type, bill_number),
     }