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/actions/bionicReading.ts

@@ -0,0 +1,74 @@
+// src/lib/actions/bionicReading.js
+
+function applyBionic(node: HTMLElement) {
+  const walker = document.createTreeWalker(node, NodeFilter.SHOW_TEXT);
+  const textNodes: Text[] = [];
+  let current: Node | null;
+  while ((current = walker.nextNode())) {
+    if (current.nodeType === Node.TEXT_NODE) textNodes.push(current as Text);
+  }
+
+  for (const textNode of textNodes) {
+    if (textNode.textContent == null) continue;
+    const words = textNode.textContent.split(/(\s+)/);
+    if (words.length <= 1 && !words[0].trim()) continue;
+
+    const fragment = document.createDocumentFragment();
+    for (const word of words) {
+      if (!word.trim() || word.length < 2) {
+        fragment.appendChild(document.createTextNode(word));
+        continue;
+      }
+      const boldLen = Math.min(3, Math.ceil(word.length / 2));
+      const b = document.createElement('b');
+      b.textContent = word.slice(0, boldLen);
+      fragment.appendChild(b);
+      fragment.appendChild(document.createTextNode(word.slice(boldLen)));
+    }
+    textNode.parentNode?.replaceChild(fragment, textNode);
+  }
+}
+
+function stripBionic(node: HTMLElement) {
+  const bolds = node.querySelectorAll("b");
+  for (const b of bolds) {
+    const text = document.createTextNode(b.textContent ?? "");
+    b.parentNode?.replaceChild(text, b);
+  }
+  node.normalize(); // merge adjacent text nodes
+}
+
+export function bionicReading(node: HTMLElement, enabled: boolean) {
+  let observer: MutationObserver | null = null;
+
+  function refresh() {
+    // Disconnect observer while we mutate, to avoid infinite loop
+    if (observer) observer.disconnect();
+    stripBionic(node);
+    if (enabled) applyBionic(node);
+    if (observer) observe();
+  }
+
+  function observe() {
+    if (!observer) return;
+    observer.observe(node, { childList: true, characterData: true, subtree: true });
+  }
+
+  // MutationObserver catches Svelte re-rendering DOM content underneath us
+  // (new transcript segments, task name edits, etc.)
+  observer = new MutationObserver(refresh);
+
+  if (enabled) applyBionic(node);
+  observe();
+
+  return {
+    update(newEnabled: boolean) {
+      enabled = newEnabled;
+      refresh();
+    },
+    destroy() {
+      if (observer) observer.disconnect();
+      stripBionic(node);
+    }
+  };
+}