Fill the remaining gaps: badge upload, radio tools, VPN, writeable boxes

Built the admin tools previously listed as missing:
- Badge upload (/admin/badges): uploads a <code>.gif into the emulator's
  badge dir via BADGE_UPLOAD_DIR (node:fs); validated code/type/size,
  logged. Made configurable rather than skipped.
- Radio tools: /admin/radio/api-keys (CRUD, server-generated keys),
  /admin/radio/autodj (Auto-DJ playlist CRUD), /admin/radio/embed (embed
  snippet generator), /admin/radio/points (points settings),
  /admin/radio/monitoring (live stream/now-playing/listeners status).
  radio_api_keys + radio_auto_dj_playlist already had real columns.
- /admin/vpn: VPN/proxy detection config (block toggle + provider + key),
  complementing /admin/ip's raw blacklist.
- Writeable boxes: new website_writeable_boxes table (model + migration
  0006) + /admin/writeable-boxes CRUD; active boxes render on the public
  home page. env: BADGE_UPLOAD_DIR.

Verified live (prod, amx_test): all 8 pages render with real data; a test
writeable box appeared on the public home and was reverted. tsc 0,
vitest 49/49, next build 0 (7 new admin routes).

src/app/admin/layout.tsx

@@ -22,6 +22,7 @@ const NAV_GROUPS: { label: string; items: { href: string; label: string }[] }[]
       { href: "/admin/navigation", label: "Navigator" },
       { href: "/admin/help-questions", label: "Help center" },
       { href: "/admin/ads", label: "Advertisements" },
+      { href: "/admin/writeable-boxes", label: "Writeable boxes" },
       { href: "/admin/photos", label: "Photos" },
     ],
   },
@@ -31,6 +32,7 @@ const NAV_GROUPS: { label: string; items: { href: string; label: string }[] }[]
       { href: "/admin/users", label: "Users" },
       { href: "/admin/bans", label: "Bans" },
       { href: "/admin/ip", label: "IP management" },
+      { href: "/admin/vpn", label: "VPN" },
       { href: "/admin/applications", label: "Applications" },
       { href: "/admin/teams", label: "Teams" },
       { href: "/admin/permissions", label: "Permissions" },