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/time.ts

@@ -0,0 +1,46 @@
+/** Pad number to 2 digits */
+export function pad(n: number): string {
+  return n.toString().padStart(2, "0");
+}
+
+/** Format seconds as M:SS (e.g. 1:05) */
+export function formatTime(seconds: number): string {
+  if (!seconds || isNaN(seconds)) return "0:00";
+  const m = Math.floor(seconds / 60);
+  const s = Math.floor(seconds % 60).toString().padStart(2, "0");
+  return `${m}:${s}`;
+}
+
+/** Format seconds as human duration (e.g. 2m 30s) */
+export function formatDuration(seconds: number): string {
+  if (!seconds) return "";
+  const m = Math.floor(seconds / 60);
+  const s = Math.round(seconds % 60);
+  return m > 0 ? `${m}m ${s}s` : `${s}s`;
+}
+
+/** Format ISO timestamp as D Mon HH:MM (e.g. 15 Mar 18:11) */
+export function formatTimestamp(iso: string | null | undefined): string {
+  if (!iso) return "";
+  const d = new Date(iso);
+  return d.toLocaleDateString("en-GB", { day: "numeric", month: "short" }) +
+    " " + d.toLocaleTimeString("en-GB", { hour: "2-digit", minute: "2-digit" });
+}
+
+/** Format seconds as SRT timestamp (HH:MM:SS,mmm) */
+export function formatTimeSRT(seconds: number): string {
+  const h = Math.floor(seconds / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  const s = Math.floor(seconds % 60);
+  const ms = Math.floor((seconds % 1) * 1000);
+  return `${pad(h)}:${pad(m)}:${pad(s)},${ms.toString().padStart(3, "0")}`;
+}
+
+/** Format seconds as VTT timestamp (HH:MM:SS.mmm) */
+export function formatTimeVTT(seconds: number): string {
+  const h = Math.floor(seconds / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  const s = Math.floor(seconds % 60);
+  const ms = Math.floor((seconds % 1) * 1000);
+  return `${pad(h)}:${pad(m)}:${pad(s)}.${ms.toString().padStart(3, "0")}`;
+}