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/HotkeyRecorder.svelte

@@ -1,4 +1,4 @@
-<script>
+<script lang="ts">
   import { settings, saveSettings } from "$lib/stores/page.svelte.js";
 
   let recording = $state(false);
@@ -6,7 +6,7 @@
 
   const modifierKeys = new Set(["Control", "Shift", "Alt", "Meta"]);
 
-  function handleKeyDown(e) {
+  function handleKeyDown(e: KeyboardEvent) {
     // Capture-phase listener; guard still belts-and-braces.
     if (!recording) return;
     e.preventDefault();
@@ -20,7 +20,7 @@
     // Wait for a non-modifier key
     if (modifierKeys.has(e.key)) return;
 
-    const parts = [];
+    const parts: string[] = [];
     if (e.ctrlKey) parts.push("Ctrl");
     if (e.shiftKey) parts.push("Shift");
     if (e.altKey) parts.push("Alt");