chore: remove cloudflare + docker + legacy migration scripts

Phase 7 cleanup of the Vercel + Upstash consolidation plan:

- delete wrangler.toml, Dockerfile, docker-compose{,.dev}.yml,
  scripts/migrate-atlas-to-upstash.js (one-shot migration done)
- drop wrangler + mongodb devDeps and migrate* npm scripts;
  regenerate package-lock.json (-70 packages)
- prune CF/Wrangler/Atlas-export entries from .gitignore + .vercelignore
- drop MONGODB_URI from .env.deploy.example
- rewrite README for Vercel + Upstash architecture
- refresh stale Cloudflare comments in src/{logger,models,repository}

src/logger.js

@@ -1,5 +1,4 @@
-// Worker-friendly structured logger. Cloudflare Observability indexes JSON
-// console output, so we emit one JSON record per call.
+// Structured JSON logger — one JSON record per call for log aggregators.
 export function createLogger() {
   function log(level, payloadOrMsg, maybeMsg) {
     const isObj = payloadOrMsg !== null && typeof payloadOrMsg === 'object';

src/models/apple-app.js

@@ -1,5 +1,5 @@
 // AppleApp cache entry — Java parity (_id=appId, class="AppleApp").
-// TTL is enforced by Cloudflare KV via expirationTtl, so no isExpired helper.
+// TTL is enforced by Upstash Redis EX, so no isExpired helper.
 export function newAppleApp(appId, response, millis) {
   return { _id: appId, class: 'AppleApp', app: response, millis };
 }

src/models/google-app.js

@@ -1,5 +1,5 @@
 // GoogleApp cache entry — Java parity (_id=appId, class="GoogleApp").
-// TTL is enforced by Cloudflare KV via expirationTtl, so no isExpired helper.
+// TTL is enforced by Upstash Redis EX, so no isExpired helper.
 export function newGoogleApp(appId, response, millis) {
   return { _id: appId, class: 'GoogleApp', app: response, millis };
 }

src/repository/upstash.js

@@ -1,6 +1,6 @@
-// Upstash Redis adapter — replaces the prior Cloudflare KV wrapper.
+// Upstash Redis adapter.
 //
-// Logical key namespace (unchanged from KV layer):
+// Logical key namespace:
 //   admin                       singleton
 //   group:{chatId}              per-group state
 //   apple:{appId}               cached Apple response (with TTL)