feat(frontend): slice 1 — foundation for MUI->shadcn migration

Web UI rework (openspec/changes/web-ui-rework). Foundation slice:
- Add @tanstack/react-table; remove orphaned recharts, d3
- Vendor shadcn primitives: tabs table dialog input label checkbox
  switch progress separator avatar textarea dropdown-menu scroll-area
- Add Vitest + @testing-library/react + jsdom harness; npm test script
- Delete no-op theme.ts shim; remove getAppTheme references
- Smoke test proves the harness

Gate: build + lint + test green.

frontend/src/index.css

@@ -23,6 +23,9 @@
 	--color-border: #e2e8f0;
 	--color-input: #e2e8f0;
 	--color-ring: #4f8cff;
+	/* Status / Grafana-link semantic cues — single source of truth for Badges.
+	   chart-1=info/brand, chart-2=success, chart-3=warning,
+	   chart-4=destructive, chart-5=neutral-accent. */
 	--color-chart-1: #4f8cff;
 	--color-chart-2: #22c55e;
 	--color-chart-3: #f59e0b;
@@ -59,6 +62,9 @@
 	--color-border: #334155;
 	--color-input: #334155;
 	--color-ring: #4f8cff;
+	/* Status / Grafana-link semantic cues — single source of truth for Badges.
+	   chart-1=info/brand, chart-2=success, chart-3=warning,
+	   chart-4=destructive, chart-5=neutral-accent. */
 	--color-chart-1: #4f8cff;
 	--color-chart-2: #22c55e;
 	--color-chart-3: #f59e0b;