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/env.ts

@@ -42,6 +42,10 @@ const schema = z.object({
     .transform((v) => v === "true" || v === "1"),
   // Hashing driver for NEW passwords: bcrypt (default, fits varchar(64)) | argon2id.
   PASSWORD_HASH: z.enum(["bcrypt", "argon2id"]).optional(),
+  // Filesystem dir the badge uploader writes <code>.gif into (the emulator's
+  // badge image folder, e.g. .../assets/c_images/album1584). Upload is disabled
+  // when unset.
+  BADGE_UPLOAD_DIR: z.string().optional(),
   // Optional AI content moderation (comments / guestbook).
   OPENAI_API_KEY: z.string().optional(),
   // Optional alerting (jobs worker / alert service).