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/ZonePicker.svelte

@@ -1,4 +1,4 @@
-<script>
+<script lang="ts">
   import { getPreferences, updatePreferences } from '$lib/stores/preferences.svelte.js';
 
   const prefs = getPreferences();
@@ -8,9 +8,9 @@
     { id: 'cave', label: 'Cave', description: 'Cool, focused', swatch: 'bg-[#141a1e]' },
     { id: 'energy', label: 'Energy', description: 'Warm, active', swatch: 'bg-[#1c1815]' },
     { id: 'reset', label: 'Reset', description: 'Natural, calm', swatch: 'bg-[#161a16]' },
-  ];
+  ] as const;
 
-  function selectZone(id) {
+  function selectZone(id: string) {
     updatePreferences({ zone: id });
   }
 </script>