fix(backend): read a tooth code whatever script its digits are in

The extraction model transcribes Persian speech, so it can hand back "۲۶"
in Persian digits or "2 6" from a digit-by-digit dictation. Both were
compared literally against /^[1-8][1-8]$/, missed, and fell through to the
positional branch with no quadrant — where the tooth was reported as "not
understood". The clinician loses a tooth and is told the words were the
problem.

normalizeFdiCode() now runs at both the branch choice and the final
validation, so the two cannot disagree. toLatinDigits moves out of
jalali.ts into common/digits.ts: it was exported but unused in production,
and a tooth module reaching into the calendar module would read as an
accident.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/src/modules/voice/extraction.wire.ts

@@ -1,3 +1,4 @@
+import { normalizeFdiCode } from '../../common/fdi';
 import type {
   ConnectedSpanIntent,
   DueIntent,
@@ -180,7 +181,10 @@ const FDI_SHAPE = /^[1-8][1-8]$/;
 
 function toToothIntent(wire: WireToothIntent | undefined | null): ToothIntent {
   const spoken = typeof wire?.spoken === 'string' ? wire.spoken : '';
-  const fdi = typeof wire?.fdi === 'string' ? wire.fdi.trim() : '';
+  // Persian digits and digit-by-digit dictation ("۲۶", "2 6") are FDI codes that do not
+  // match literally; without normalising first they fall through to the positional branch
+  // with no quadrant and are reported as unresolved.
+  const fdi = normalizeFdiCode(wire?.fdi);
   // Only take the explicit branch for something actually FDI-shaped. A model that emits
   // fdi:"6" alongside correct arch/side/position would otherwise lose the tooth entirely.
   if (FDI_SHAPE.test(fdi)) {