Implement M1 authoring loop: library, editor, live preview, persistence

M1 MVP from docs/IMPLEMENTATION-PLAN.md, with the /alignment pass applied.

- core: Snippet model + factory; prepareSpecForRender (copy-not-mutate); per-theme Vega chart config
- state/orchestration: SnippetStore with debounced auto-save; IndexedDB adapter + read-time migration; startup hydration + write-through persistence
- ui: SnippetLibrary, SpecEditor (Monaco edcore.main — full editor features, JSON-only languages), LivePreview
- build: Monaco/Vega manual chunks; raised PWA precache ceiling
- alignment: flush a valid draft on snippet switch (+regression tests); TODO breadcrumbs for the preview render race and the window.confirm delete
- housekeeping: gitignore .claude/projects/

src/app/App.tsx

@@ -1,12 +1,15 @@
+import { LivePreview } from './components/LivePreview';
+import { SnippetLibrary } from './components/SnippetLibrary';
+import { SpecEditor } from './components/SpecEditor';
 import styles from './App.module.css';
 
 /**
  * Application shell — the three-pane workspace from spec §01A
  * (library · editor · preview) under a fixed header.
  *
- * This is the skeleton: panes are placeholders. Each milestone fills one in
- * (see docs/IMPLEMENTATION-PLAN.md). Resizing, toggling, modals, routing, and
- * shortcuts arrive in later milestones.
+ * M1 fills the panes with the MVP authoring loop. Pane resizing/toggling,
+ * modals, routing, and shortcuts arrive in later milestones (see
+ * docs/IMPLEMENTATION-PLAN.md).
  */
 export function App() {
   return (
@@ -19,13 +22,13 @@ export function App() {
 
       <main className={styles.panes}>
         <section className={styles.pane} aria-label="Snippet library">
-          <div className={styles.paneLabel}>Library</div>
+          <SnippetLibrary />
         </section>
-        <section className={styles.pane} aria-label="Spec editor">
-          <div className={styles.paneLabel}>Editor</div>
+        <section className={styles.paneEditor} aria-label="Spec editor">
+          <SpecEditor />
         </section>
         <section className={styles.pane} aria-label="Live preview">
-          <div className={styles.paneLabel}>Preview</div>
+          <LivePreview />
         </section>
       </main>
     </div>