fix: handle within-page cosponsor duplicates from Congress.gov API

Congress.gov occasionally returns the same member twice on a single page
with different sponsorship dates (observed: Sen. Warnock on 119-s-1383).
The DB uniqueness check didn't catch this because the first insert hadn't
been committed yet when processing the duplicate row, causing a
UniqueViolation. Fix adds an `inserted_this_run` set to skip bioguide_ids
already added in the current fetch loop.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/workers/bill_classifier.py

@@ -140,6 +140,9 @@ def fetch_bill_cosponsors(self, bill_id: str):
             return {"status": "skipped"}
 
         known_bioguides = {row[0] for row in db.execute(text("SELECT bioguide_id FROM members")).fetchall()}
+        # Track bioguide_ids already inserted this run to handle within-page dupes
+        # (Congress.gov sometimes lists the same member twice with different dates)
+        inserted_this_run: set[str] = set()
         inserted = 0
         offset = 0
 
@@ -157,12 +160,15 @@ def fetch_bill_cosponsors(self, bill_id: str):
                 if bioguide_id and bioguide_id not in known_bioguides:
                     bioguide_id = None
 
-                # Skip if we already have this (bioguide_id, bill_id) pair
+                # Skip dupes — both across runs (DB check) and within this page
                 if bioguide_id:
+                    if bioguide_id in inserted_this_run:
+                        continue
                     exists = db.query(BillCosponsor).filter_by(
                         bill_id=bill_id, bioguide_id=bioguide_id
                     ).first()
                     if exists:
+                        inserted_this_run.add(bioguide_id)
                         continue
 
                 date_str = cs.get("sponsorshipDate")
@@ -179,6 +185,8 @@ def fetch_bill_cosponsors(self, bill_id: str):
                     state=cs.get("state"),
                     sponsored_date=sponsored_date,
                 ))
+                if bioguide_id:
+                    inserted_this_run.add(bioguide_id)
                 inserted += 1
 
             db.commit()