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.

lib/db/scripts/pre-push-cleanup.ts

@@ -85,8 +85,9 @@ async function main(): Promise<void> {
     // NOT NULL + unique constraint on protocol_room_bookings.booking_reference.
     // Without this, pushing the constraint against a populated table (any
     // pre-existing booking predates the column) would fail. Reference format
-    // mirrors makeBookingReference() in the API: RB-{year}-{pad4(id)}, which
-    // is unique because id is unique. Idempotent: only touches NULL rows.
+    // mirrors makeBookingReference() in the API: {year}-{pad4(id)} (digits
+    // only, no letters), which is unique because id is unique. Idempotent:
+    // fills NULL rows and normalizes any legacy "RB-" prefixed rows.
     if (await tableExists(client, "protocol_room_bookings")) {
       const hasColumn = await client.query(
         `SELECT 1 FROM information_schema.columns
@@ -98,10 +99,21 @@ async function main(): Promise<void> {
         const backfilled = await client.query(
           `UPDATE protocol_room_bookings
               SET booking_reference =
-                'RB-' || EXTRACT(YEAR FROM created_at)::int
+                EXTRACT(YEAR FROM created_at)::int
                      || '-' || LPAD(id::text, 4, '0')
             WHERE booking_reference IS NULL`,
         );
+        const normalized = await client.query(
+          `UPDATE protocol_room_bookings
+              SET booking_reference = regexp_replace(booking_reference, '^RB-', '')
+            WHERE booking_reference LIKE 'RB-%'`,
+        );
+        const stripped = normalized.rowCount ?? 0;
+        if (stripped > 0) {
+          console.log(
+            `[pre-push] Normalized ${stripped} legacy RB- booking_reference value(s) to digits-only.`,
+          );
+        }
         const filled = backfilled.rowCount ?? 0;
         if (filled > 0) {
           console.log(