feat: add bank file import as core, move Enable Banking to extension

Replace PSD2 bank integration as the default with file-based bank
import (CSV/XML), which better suits Swedish sole traders and small
companies. Enable Banking is now an opt-in extension.

- Phase 1: Extract generic transaction ingestion service (ingest.ts)
  with dedup, auto-categorization, and OCR-based invoice matching
- Phase 2: Bank file parser library supporting Nordea, SEB, Swedbank,
  Handelsbanken CSV formats and ISO 20022 camt.053 XML
- Phase 3: Database migration adding import_source, reference columns
  and bank_file_imports tracking table
- Phase 4: Import wizard UI (5-step flow) and API routes for parse/execute
- Phase 5: Move Enable Banking to extensions/enable-banking/ with
  commented-out loader entry for opt-in activation
- Phase 6: 104 new tests (ingestion + all parser formats), fixing
  Nordea detection overlap and camt.053 XML tag collision bugs

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

vercel.json

@@ -17,7 +17,7 @@
       "schedule": "0 0 2 1 *"
     },
     {
-      "path": "/api/banking/sync/cron",
+      "path": "/api/extensions/enable-banking/sync/cron",
       "schedule": "0 5 * * *"
     },
     {