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.module.css

@@ -39,20 +39,26 @@
 }
 
 .pane {
-  flex: 1;
+  flex: 1 1 0;
   min-width: 0;
   padding: var(--space-4);
   overflow: auto;
   border-right: 1px solid var(--color-border);
 }
 
+/* Library is a fixed-ish sidebar; editor + preview share the rest. */
+.panes > .pane:first-child {
+  flex: 0 0 260px;
+}
+
+/* Editor pane: Monaco manages its own scroll/layout, so no padding. */
+.paneEditor {
+  flex: 1 1 0;
+  min-width: 0;
+  overflow: hidden;
+  border-right: 1px solid var(--color-border);
+}
+
 .pane:last-child {
   border-right: none;
 }
-
-.paneLabel {
-  font-size: 11px;
-  text-transform: uppercase;
-  letter-spacing: 0.05em;
-  color: var(--color-text-muted);
-}