site: add Astro frontend — login, register, reset-password, invites, home

Step 8 of the migration plan. Minimal Astro + Tailwind site (no Svelte).
Pages:
- / (home): post-login card grid, shows Activity/Wiki/Planner cards based
  on wiki_access / activity_access from /api/me; URLs via PUBLIC_* env vars
- /login/: JWT cookie issued on success; ?next= redirect supported
- /register/: invite-code flow, auto-fills code from ?code= param
- /reset-password/: admin-issued code flow; disables form on success
- /invites/: list + generate invites; activity-access toggle for eligible users

Base layout: minimal nav with handle + sign-out, auth wall (/api/me check),
race-calendar accent palette, dark/light theme tokens.

site/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "bincio-auth-site",
+  "type": "module",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "astro dev",
+    "build": "astro build",
+    "preview": "astro preview",
+    "astro": "astro"
+  },
+  "dependencies": {
+    "@astrojs/tailwind": "^5.1.0",
+    "astro": "^5.0.0",
+    "tailwindcss": "^3.4.0"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "typescript": "^5.7.0"
+  }
+}