fix(store): enforce sighting finding id invariant

skills/last30days/scripts/store.py

@@ -163,7 +163,7 @@ MIGRATIONS: Dict[int, str] = {
     2: """
 CREATE TABLE IF NOT EXISTS finding_sightings (
     id INTEGER PRIMARY KEY,
-    finding_id INTEGER REFERENCES findings(id) ON DELETE CASCADE,
+    finding_id INTEGER NOT NULL REFERENCES findings(id) ON DELETE CASCADE,
     run_id INTEGER REFERENCES research_runs(id) ON DELETE CASCADE,
     topic_id INTEGER REFERENCES topics(id) ON DELETE CASCADE,
     source TEXT NOT NULL,

tests/test_store.py

@@ -451,9 +451,14 @@ def test_init_db_creates_finding_sightings_table(temp_db):
     table = conn.execute(
         "SELECT name FROM sqlite_master WHERE type='table' AND name='finding_sightings'"
     ).fetchone()
+    columns = {
+        row[1]: row[3]
+        for row in conn.execute("PRAGMA table_info(finding_sightings)").fetchall()
+    }
     conn.close()
 
     assert table is not None
+    assert columns["finding_id"] == 1
 
 
 def test_store_findings_records_sightings_for_new_findings(temp_db):