feat(persistence): v19 schema — fire enrichment columns

Add nullable fire_cause, unique_fire_id, geocoder_city columns to the
fires table (additive migration, no backfill) and bump SCHEMA_VERSION
18 -> 19. Validated in production on CT 108 (schema_meta.version=19,
clean run); commits the finished fire-spam/danger-zones migration that
was live but uncommitted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

work/meshai/persistence/db.py

@@ -30,7 +30,7 @@ logger = logging.getLogger(__name__)
 
 DEFAULT_DB_PATH = "/data/meshai.sqlite"
 MESHAI_DB_PATH_ENV = "MESHAI_DB_PATH"
-SCHEMA_VERSION = 18
+SCHEMA_VERSION = 19
 SCHEMA_META_TABLE = "schema_meta"
 MIGRATIONS_DIR = Path(__file__).parent / "migrations"
 

work/meshai/persistence/migrations/v19.sql

@@ -0,0 +1,6 @@
+-- v19: fire_cause, unique_fire_id, geocoder_city columns for fire-alert enrichment.
+-- Nullable TEXT, no index, no backfill.
+
+ALTER TABLE fires ADD COLUMN fire_cause     TEXT;
+ALTER TABLE fires ADD COLUMN unique_fire_id TEXT;
+ALTER TABLE fires ADD COLUMN geocoder_city  TEXT;