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/core/vega-themes.ts

@@ -0,0 +1,60 @@
+/**
+ * Vega-Lite chart config per UI theme (docs/architecture/05 §3).
+ *
+ * Portable core: a Vega-Lite `Config` styles every chart globally so charts
+ * visually belong to the app rather than looking like stock Vega-Lite. This is
+ * the single source of truth mapping a `UiTheme` to a config; it is applied at
+ * embed time (never baked into the user's stored spec). Adding a UI theme = one
+ * config object plus one map entry here.
+ */
+
+import type { Config } from 'vega-lite';
+import type { UiTheme } from './theme';
+
+export const lightChartConfig: Config = {
+  background: 'transparent',
+  font: '"Inter", system-ui, sans-serif',
+  title: { fontSize: 15, fontWeight: 600, color: '#1c1c1e' },
+  axis: {
+    domainColor: '#1c1c1e',
+    gridColor: '#e4e4e7',
+    gridDash: [3, 3],
+    labelColor: '#52525b',
+    titleColor: '#1c1c1e',
+    labelFontSize: 11,
+    titleFontSize: 12,
+  },
+  range: {
+    category: ['#2f6df6', '#f5a524', '#17b890', '#e5484d', '#8b5cf6', '#0ea5e9'],
+  },
+  view: { stroke: 'transparent' },
+};
+
+export const experimentalChartConfig: Config = {
+  background: 'transparent',
+  font: '"Inter", system-ui, sans-serif',
+  title: { fontSize: 15, fontWeight: 600, color: '#f4f4f5' },
+  axis: {
+    domainColor: '#a1a1aa',
+    gridColor: '#3f3f46',
+    gridDash: [3, 3],
+    labelColor: '#a1a1aa',
+    titleColor: '#f4f4f5',
+    labelFontSize: 11,
+    titleFontSize: 12,
+  },
+  range: {
+    category: ['#5b8def', '#f5a524', '#2dd4a7', '#f0666b', '#a78bfa', '#38bdf8'],
+  },
+  view: { stroke: 'transparent' },
+};
+
+const CHART_CONFIG: Record<UiTheme, Config> = {
+  light: lightChartConfig,
+  experimental: experimentalChartConfig,
+};
+
+/** The Vega-Lite config for a UI theme — the only theme → config mapping. */
+export function chartConfigFor(theme: UiTheme): Config {
+  return CHART_CONFIG[theme];
+}