refactor(frontend): migrate JS modules to TypeScript

Wholesale JS -> TS migration of the frontend — stores, utils, actions,
and all Svelte component scripts adopt type annotations. Compile-time
surfaces (app.d.ts, lib/types/) added for shared DTO types.

Build plumbing:
  - package.json: dev:frontend script that runs svelte-kit sync first
  - tauri.conf.json: beforeDevCommand points at dev:frontend
  - run.sh: dropped the sed-hack that temporarily blanked beforeDevCommand;
    now relies on npm run dev:frontend to avoid double-Vite
  - jsconfig.json: allowImportingTsExtensions

Preserves all Group 1 behaviour:
  - page.svelte.ts keeps loadHistory / loadTasks Tauri-first, no
    localStorage; saveTranscriptMeta + mapTranscriptRow + mapTaskRow
    intact; update_task_cmd and update_transcript_meta_cmd invocations
    carry the correct payload shape.
  - Toasts, preferences stores typed without behaviour change.
  - Viewer still routes segment edits through saveTranscriptMeta; the
    Task 1.5 TODO markers are gone.

taskExtractor.ts is functionally improved during the migration:
  - multi-task matches in the same sentence
  - list-style shopping-verb expansion (get bread, milk, and cheese)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/utils/accessibilityTypography.ts

@@ -0,0 +1,41 @@
+import type { AccessibilityPreferences, FontFamily } from "$lib/types/app";
+
+const PRETEXT_FONT_FAMILIES = {
+  lexend: "'Lexend'",
+  atkinson: "'Atkinson Hyperlegible Next'",
+  opendyslexic: "'OpenDyslexic'",
+} satisfies Record<FontFamily, string>;
+
+export function pretextFontFamily(fontFamily: FontFamily = "lexend"): string {
+  return PRETEXT_FONT_FAMILIES[fontFamily] || PRETEXT_FONT_FAMILIES.lexend;
+}
+
+export function pretextFontShorthand(
+  accessibility: Partial<AccessibilityPreferences> = {},
+  sizePx = 16,
+): string {
+  return `${sizePx}px ${pretextFontFamily(accessibility.fontFamily)}`;
+}
+
+export function bodyPretextLineHeight(
+  accessibility: Partial<AccessibilityPreferences> = {},
+  sizePx = 16,
+): number {
+  const ratio = accessibility.lineHeight || 1.5;
+  return Math.round(sizePx * ratio);
+}
+
+export function transcriptPretextFont(
+  accessibility: Partial<AccessibilityPreferences> = {},
+): string {
+  const sizePx = accessibility.transcriptSize || accessibility.fontSize || 16;
+  return pretextFontShorthand(accessibility, sizePx);
+}
+
+export function transcriptPretextLineHeight(
+  accessibility: Partial<AccessibilityPreferences> = {},
+  ratio = 1.85,
+): number {
+  const sizePx = accessibility.transcriptSize || accessibility.fontSize || 16;
+  return Math.round(sizePx * ratio);
+}