feat: planning structure + task 1.2 stack rounding-out

Add .planning/ scaffolding:
- ROADMAP.md (4 phases, 8 non-negotiable design rules)
- phase-1-foundation/ README + 9 task files (1.2-1.10)
- phase-2-live-map / phase-3-dogfood-readiness / phase-4-future README placeholders

Task 1.2 — stack rounding-out:
- Tailwind 4 via @tailwindcss/vite + src/styles/globals.css
- shadcn/ui (slate, new-york) primitives in src/ui/primitives/:
  button, input, label, form, card, alert
- TanStack Router 1.169 + Query 5.100 (devtools + plugin in devDeps)
- Zustand 5, @directus/sdk 21, zod 4, react-hook-form 7 + resolvers
- Prettier 3 + eslint-config-prettier + eslint-plugin-prettier
- ESLint override disabling react-refresh/only-export-components for
  src/ui/primitives/** (intentional dual-exports in shadcn primitives)
- Path alias @/* -> ./src/* in tsconfig.json + tsconfig.app.json
  (TS 6 deprecates baseUrl; paths now resolve relative to config file).
  Pulled forward from 1.3 because shadcn add CLI needs it resolvable.
- Scripts: dev, build, preview, lint, typecheck, format, format:check,
  test (placeholder)
- App.tsx Tailwind smoke test (centred card + shadcn Button)
- README.md rewritten with stack/scripts/shadcn-add docs

All four gates green: typecheck, lint, format:check, build (222KB / 70KB gz).

tsconfig.app.json

@@ -15,6 +15,11 @@
     "noEmit": true,
     "jsx": "react-jsx",
 
+    /* Path aliases (TS 6+: paths resolve relative to the config file; no baseUrl) */
+    "paths": {
+      "@/*": ["./src/*"]
+    },
+
     /* Linting */
     "noUnusedLocals": true,
     "noUnusedParameters": true,