docs: cut the comments that were not earning their place

I wrote 731 comment lines on this branch against 4,530 lines of code — 14%,
where the rest of the repo runs at 1.8%. CLAUDE.md asks for code that reads
like its surroundings, and this did not.

Removed by genre rather than by taste:

- restating the code, e.g. "JS getUTCDay() numbering: Sunday = 0" above the
  map that literally shows it, and a docblock on startOfWeek explaining that
  it returns the start of the week;
- narrating history — "this used to rebuild the whole map", "left the bar
  recording forever" — which the commit message and git blame already carry;
- saying the same thing in several places: the "cannot record is not a
  denied microphone" reason appeared three times in one file, and the
  "aborting stops a per-minute metered call" reason across three files. Each
  now lives once, where the behaviour it explains lives;
- defending decisions nobody would question, like why toLatinDigits is its
  own module;
- over-explaining defensive branches, three separate comments to distinguish
  null from missing-kind from unrecognised-kind.

What stays is what the code cannot say: the patient-right convention in
toFdi, whose failure mode is a valid code for the wrong tooth; the
"this"-vs-"next" week anchoring; StrictMode re-arming mountedRef; Safari
accepting no mimeType hint; and the invariants whose violation already cost
a bug — the body parser's middleware ordering and the dispatch panel's
auto-fill rules.

Comments only. The diff contains no non-comment line.

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

backend/src/common/fdi.ts

@@ -14,10 +14,9 @@ export type Arch = 'upper' | 'lower';
 export type PatientSide = 'patient_right' | 'patient_left';
 
 /**
- * Upper arch in chart order: patient's RIGHT (18) → midline → patient's LEFT (28).
- * That is the drawn left-to-right layout, which is the mirror of the patient's own sides.
- * Do not read a tooth position off this array by index — use `toFdi()`, which owns the
- * side convention.
+ * Upper arch in chart order: patient's RIGHT (18) → midline → patient's LEFT (28) — the drawn
+ * layout, which mirrors the patient's own sides. Never read a position off this array by
+ * index; use `toFdi()`, which owns the side convention.
  */
 export const FDI_UPPER_ARCH_ORDER = [
   '18',
@@ -68,12 +67,9 @@ export function isFdiTooth(value: unknown): value is string {
 }
 
 /**
- * Clean up a tooth code the extraction model echoed back, before it is matched.
- *
- * The model is transcribing Persian speech, so it can hand back "۲۶" in Persian digits or
- * "2 6" from a digit-by-digit dictation. Neither matches an FDI code literally, and a
- * near-miss here does not fail loudly — the tooth quietly turns into "not understood".
- * Returns '' for anything that is not a string.
+ * Clean up a tooth code the model echoed back. It is reading Persian speech, so it can hand
+ * back "۲۶" or "2 6" from digit-by-digit dictation; neither matches literally, and the
+ * near-miss does not fail loudly — the tooth just turns into "not understood".
  */
 export function normalizeFdiCode(value: unknown): string {
   if (typeof value !== 'string') return '';
@@ -114,9 +110,8 @@ export function teethBetweenInclusive(a: string, b: string): string[] | null {
 /**
  * Arch + patient side + position (1 = central incisor … 8 = third molar) → FDI code.
  *
- * This function is the single place the patient-right convention lives. Getting it
- * backwards mirrors every quadrant and produces a valid-looking code for the wrong tooth,
- * which no schema check can catch — hence the exhaustive test coverage.
+ * The single place the patient-right convention lives. Getting it backwards mirrors every
+ * quadrant into a valid-looking code for the wrong tooth, which no schema check can catch.
  */
 export function toFdi(
   arch: Arch,
@@ -135,8 +130,8 @@ export function toFdi(
 }
 
 /**
- * Sort teeth along the arch, not lexically — a bridge reads 16-15-14, and 11 sits beside
- * 21 across the midline. Teeth from another arch (or unknown) sort to the end, stably.
+ * Along the arch, not lexically — a bridge reads 16-15-14, and 11 sits beside 21 across the
+ * midline. Teeth from another arch sort to the end, stably.
  */
 export function sortInArchOrder(teeth: readonly string[]): string[] {
   if (teeth.length === 0) return [];