fix: correct FINRA URL, filename format, parser column order, and default base URL

- Fix default base URL: https://cdn.finra.org/equity/regsho/daily (was www.finra.org/sites/default/files)
- Fix filename pattern: CNMSshvol{YYYYMMDD}.txt (was CAshvol with year/month subdir)
- Fix parser: actual file columns are Date|Symbol|ShortVolume|ShortExemptVolume|TotalVolume|Market
  (was incorrectly expecting Market|Symbol|... — first col is Date, last col is Market)
- Dedupe by symbol (volume is total across all listed exchanges, not per-exchange)
- Store combined market codes (e.g. 'B,Q,N') as exchange string
- Use BEGIN/COMMIT instead of db.transaction() (node:sqlite DatabaseSync doesn't have transaction())
- Update finra_config defaults in schema.sql + migration + admin fallback

app/server/src/db/schema.sql

@@ -698,6 +698,6 @@ CREATE INDEX IF NOT EXISTS idx_finra_settlement ON finra_short_interest(settleme
 -- FINRA download configuration (admin-configurable URL).
 CREATE TABLE IF NOT EXISTS finra_config (
   id          TEXT PRIMARY KEY DEFAULT 'singleton',
-  base_url    TEXT NOT NULL DEFAULT 'https://www.finra.org/sites/default/files',
+  base_url    TEXT NOT NULL DEFAULT 'https://cdn.finra.org/equity/regsho/daily',
   updated_at  TEXT NOT NULL
 );