chore(cleanup): trim 13 dead exports surfaced by knip

Narrow each helper's visibility to its actual reach instead of leaving
it exported "just in case":

  - Drop the `export` keyword on file-local helpers / constants:
    `getTrendSentiment`, `isPRWithin30Days`, `buildCoachMetricSourceType`,
    `countPassedSchedules`, `getGithubConfig`, `isComparisonBaseline`,
    `DASHBOARD_LAYOUT_VERSION`, `INTL_LOCALE_MAP`, `SIDE_EFFECT_NOTES_MAX`,
    `MEDICATION_CATEGORIES`, `openApiBase`, `ALL_MOOD_GRANULARITIES`.
  - Remove never-used dead code:
    `CodexOAuthNotConfiguredError` (declared as a backwards-compat shim
    no caller ever consumed), `editMessageReplyMarkup` (Telegram method
    nothing on the bot dispatch tree calls), and the stale
    `DISPLAY_TIMEZONE` re-export from `src/lib/format.ts`.

Knip drops from 48 -> 35 unused exports. Pure narrowing / deletion;
no behaviour change.

src/components/charts/trend-card.tsx

@@ -64,7 +64,7 @@ export type TrendDirectionSentiment = "up-good" | "up-bad" | "neutral";
  */
 export type TrendSentimentDirection = "positive" | "negative" | "neutral";
 
-export function getTrendSentiment(
+function getTrendSentiment(
   change: number | null | undefined,
   sentiment: TrendDirectionSentiment,
 ): TrendSentimentDirection {

src/components/insights/personal-record-badge.tsx

@@ -52,14 +52,12 @@ interface PersonalRecordBadgeProps {
 const THIRTY_DAYS_MS = 30 * 24 * 60 * 60 * 1000;
 
 /**
- * Pure freshness check — exported for unit testing so the component
- * itself stays free of clock calls (the React purity linter rejects
- * `Date.now()` inside a component body or hook initializer). Callers
- * pass a `now` reference; consumers in production read it from the
- * surrounding query refetch boundary where one stale-time tick =
- * one new clock reading.
+ * Pure freshness check kept out of the component body so the React
+ * purity linter doesn't trip on the `Date.now()` reference; callers
+ * pass `now` from the surrounding query refetch boundary where one
+ * stale-time tick = one new clock reading.
  */
-export function isPRWithin30Days(achievedAtIso: string, now: number): boolean {
+function isPRWithin30Days(achievedAtIso: string, now: number): boolean {
   const ts = new Date(achievedAtIso).getTime();
   return Number.isFinite(ts) && now - ts <= THIRTY_DAYS_MS;
 }