feat(backend): offer the candidate teeth for an unspecified quadrant

A tooth the resolver refuses to guess at is currently a dead end: the sheet
says the quadrant was missing and the clinician has to leave and find the
tooth on the chart. But the readings are enumerable — "دو" is one of four
teeth, "دو بالا" one of two — so unresolved items now carry them.

Narrowed by whatever was actually said, so this stays a choice offered to
the clinician rather than a guess made for them. Only tooth_missing_quadrant
carries candidates; a wrong position or a deciduous tooth has nothing to
choose between.

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

backend/src/modules/voice/tooth-intent.resolver.spec.ts

@@ -173,10 +173,47 @@ describe('resolveToothIntents', () => {
     const result = resolveToothIntents([bare]);
     expect(result.teeth).toEqual([]);
     expect(result.unresolved).toEqual([
-      { spoken: 'دندون دو', reason: 'tooth_missing_quadrant' },
+      {
+        spoken: 'دندون دو',
+        reason: 'tooth_missing_quadrant',
+        // Every reading of "position 2", for the clinician to pick from.
+        candidates: ['12', '22', '32', '42'],
+      },
     ]);
   });
 
+  it('narrows the candidates by whatever the clinician did say', () => {
+    const half = (arch: string | null, side: string | null) =>
+      resolveToothIntents([
+        {
+          kind: 'positional',
+          arch,
+          side,
+          position: 2,
+          spoken: 'دو',
+        } as unknown as ToothIntent,
+      ]).unresolved[0].candidates;
+
+    expect(half('upper', null)).toEqual(['12', '22']);
+    expect(half('lower', null)).toEqual(['32', '42']);
+    // Quadrant 1 is the patient's upper right, 4 the lower right.
+    expect(half(null, 'patient_right')).toEqual(['12', '42']);
+    expect(half(null, 'patient_left')).toEqual(['22', '32']);
+  });
+
+  it('offers no candidates for a reason a choice cannot settle', () => {
+    // Nothing to choose between when the position itself was wrong, or the tooth is
+    // deciduous — offering chips there would invent options.
+    for (const intent of [
+      positional('upper', 'patient_right', 9, 'نه'),
+      explicit('51', 'شیری'),
+    ]) {
+      expect(
+        resolveToothIntents([intent]).unresolved[0].candidates,
+      ).toBeUndefined();
+    }
+  });
+
   it('reports a missing quadrant for a half-specified tooth too', () => {
     // "دو بالا" narrows it to 12 or 22 — still not one tooth, and still not our guess.
     for (const half of [