Task #735: booking reference digits-only (no letters)

- makeBookingReference in artifacts/api-server/src/routes/protocol.ts now
  returns `${year}-${pad4(id)}` instead of `RB-${year}-${pad4(id)}`.
- Backfilled 7 existing dev DB rows: stripped "RB-" prefix via
  regexp_replace; verified 0 rows contain letters, unique/NOT NULL intact.
- lib/db/scripts/pre-push-cleanup.ts updated (architect-review finding):
  NULL backfill now uses digits-only format, plus a new idempotent
  normalization step that strips legacy "RB-" prefixes on every push.
- Frontend unchanged: bookingNumber() already strips non-digits; details
  card and public booking success page display the raw reference which is
  now digits-only. ilike search still works.
- tsc clean for tx-os and lib/db; API workflow restarted.

artifacts/api-server/src/routes/protocol.ts

@@ -442,10 +442,10 @@ async function lockRoomRow(
 }
 
 // Build a human-friendly booking reference (رقم الحجز) from a row id and its
-// creation date, e.g. "RB-2026-0042". Deterministic + unique because the id
-// is unique.
+// creation date, e.g. "2026-0042". Digits only (no letters, per user
+// request). Deterministic + unique because the id is unique.
 function makeBookingReference(id: number, when: Date): string {
-  return `RB-${when.getFullYear()}-${String(id).padStart(4, "0")}`;
+  return `${when.getFullYear()}-${String(id).padStart(4, "0")}`;
 }
 
 // Reserve the next booking id from the table's serial sequence so we can