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/components/Titlebar.svelte

@@ -1,4 +1,4 @@
-<script>
+<script lang="ts">
   import { getCurrentWindow } from "@tauri-apps/api/window";
   import { settings } from "$lib/stores/page.svelte.js";
 
@@ -19,16 +19,16 @@
     await getCurrentWindow().hide();
   }
 
-  function handleDragStart(e) {
+  function handleDragStart(e: PointerEvent) {
     if (e.button !== 0) return;
-    if (e.target.closest("button")) return;
-    try { e.currentTarget?.setPointerCapture?.(e.pointerId); } catch {}
+    if ((e.target as HTMLElement | null)?.closest("button")) return;
+    try { (e.currentTarget as HTMLElement | null)?.setPointerCapture?.(e.pointerId); } catch {}
     getCurrentWindow().startDragging();
   }
 
   // Track maximise state
   $effect(() => {
-    let unlisten;
+    let unlisten: (() => void) | undefined;
     getCurrentWindow().onResized(async () => {
       maximised = await getCurrentWindow().isMaximized();
     }).then((fn) => unlisten = fn);
@@ -36,6 +36,7 @@
   });
 </script>
 
+<!-- svelte-ignore a11y_no_static_element_interactions -->
 <div
   class="flex items-center select-none bg-sidebar border-b border-border-subtle
     {compact ? 'h-[28px]' : 'h-[32px]'}"