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/UnicodeSpinner.svelte

@@ -1,7 +1,11 @@
-<script>
-  import { onMount, onDestroy } from "svelte";
+<script lang="ts">
+  type SpinnerType = "dots" | "circle" | "pulse" | "stars" | "orbit";
 
-  let { type = "dots", speed = 100, classes = "" } = $props();
+  let { type = "dots", speed = 100, classes = "" } = $props<{
+    type?: SpinnerType;
+    speed?: number;
+    classes?: string;
+  }>();
 
   const sequences = {
     dots: ["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"],
@@ -12,17 +16,14 @@
   };
 
   let frame = $state(0);
-  let interval = null;
-  let chars = sequences[type] || sequences.dots;
+  let chars = $derived(sequences[type as SpinnerType] ?? sequences.dots);
 
-  onMount(() => {
-    interval = setInterval(() => {
+  $effect(() => {
+    frame = 0;
+    const interval = setInterval(() => {
       frame = (frame + 1) % chars.length;
     }, speed);
-  });
-
-  onDestroy(() => {
-    if (interval) clearInterval(interval);
+    return () => clearInterval(interval);
   });
 </script>