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/MicroSteps.svelte

@@ -1,10 +1,16 @@
-<script>
+<script lang="ts">
   import { invoke } from '@tauri-apps/api/core';
   import { ListTree, Check, Timer, Loader2 } from 'lucide-svelte';
 
   let { parentTaskId, reduceMotion = false } = $props();
 
-  let subtasks = $state([]);
+  interface Subtask {
+    id: string;
+    text: string;
+    done: boolean;
+  }
+
+  let subtasks = $state<Subtask[]>([]);
   let loading = $state(false);
   let error = $state('');
   let decomposing = $state(false);
@@ -13,7 +19,7 @@
     loading = true;
     error = '';
     try {
-      subtasks = await invoke('list_subtasks_cmd', { parentTaskId });
+      subtasks = await invoke<Subtask[]>('list_subtasks_cmd', { parentTaskId });
     } catch (e) {
       error = String(e);
     } finally {
@@ -25,7 +31,7 @@
     decomposing = true;
     error = '';
     try {
-      subtasks = await invoke('decompose_and_store', { parentTaskId });
+      subtasks = await invoke<Subtask[]>('decompose_and_store', { parentTaskId });
     } catch (e) {
       error = String(e);
     } finally {
@@ -33,7 +39,7 @@
     }
   }
 
-  async function checkStep(subtaskId) {
+  async function checkStep(subtaskId: string) {
     try {
       await invoke('complete_subtask_cmd', { subtaskId });
       const idx = subtasks.findIndex(s => s.id === subtaskId);
@@ -41,7 +47,7 @@
     } catch (_) {}
   }
 
-  function startTimer(subtaskId) {
+  function startTimer(subtaskId: string) {
     window.dispatchEvent(new CustomEvent('kon:start-timer', {
       detail: { taskId: subtaskId, seconds: 120 }
     }));