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/components/LivePreview.module.css

@@ -0,0 +1,24 @@
+.preview {
+  height: 100%;
+  width: 100%;
+  overflow: auto;
+}
+
+.chart {
+  display: flex;
+  align-items: flex-start;
+  justify-content: center;
+  min-height: 100%;
+  padding: var(--space-2);
+}
+
+.error {
+  margin: 0;
+  padding: var(--space-3);
+  font-family: var(--font-mono);
+  font-size: 12px;
+  line-height: 1.5;
+  color: var(--color-error);
+  white-space: pre-wrap;
+  word-break: break-word;
+}