feat(backend): read a spoken tooth number as its FDI code

The prompt had this backwards. "Never output an FDI tooth code unless the
speaker used FDI notation. Prefer arch + side + position" pushed the model
to decompose speech into "upper / patient_right / six", so the clinician
effectively had to *describe* every tooth. Saying "دندون بیست و شش" — the
way a dentist actually dictates — was the unsupported path.

FDI is what clinicians speak, so the prompt now teaches the notation
instead of forbidding it: first digit = quadrant from the patient's own
point of view, second digit = position from the midline. arch/side/position
stays as the reading of a *described* tooth, where a single digit is a
position and the quadrant comes from words.

Two guards come with it, because bare numbers are now teeth: a single digit
alone still refuses to guess a quadrant, and dates, counts and quantities
are explicitly not teeth.

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

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

@@ -21,7 +21,7 @@ import { WEEKDAYS } from './voice.types';
 
 export type WireToothIntent = {
   spoken: string;
-  /** Two-digit FDI code, only when the speaker genuinely used FDI notation. */
+  /** The two-digit FDI code the clinician spoke; null when the tooth was described. */
   fdi: string | null;
   arch: 'upper' | 'lower' | null;
   side: 'patient_right' | 'patient_left' | null;
@@ -66,7 +66,8 @@ const TOOTH_SCHEMA = {
     fdi: {
       type: ['string', 'null'],
       description:
-        'Two-digit FDI code ONLY if the speaker used FDI notation. Otherwise null.',
+        'The two-digit FDI code the clinician said for this tooth, e.g. "26". Null only ' +
+        'when the tooth was described in words instead of numbered.',
     },
     arch: { type: ['string', 'null'], enum: ['upper', 'lower', null] },
     side: {
@@ -76,7 +77,8 @@ const TOOTH_SCHEMA = {
     },
     position: {
       type: ['integer', 'null'],
-      description: '1 = central incisor … 8 = third molar.',
+      description:
+        'Position from the midline: 1 = central incisor … 8 = third molar. Never an FDI code.',
     },
   },
 } as const;