refactor: merge BOT_TOKEN + ADDITIONAL_BOT_TOKENS into single BOT_TOKENS env + speed audit

BOT_TOKENS env:
- Single BOT_TOKENS env var (comma-separated) replaces BOT_TOKEN + ADDITIONAL_BOT_TOKENS
- Backward compat: falls back to BOT_TOKEN + ADDITIONAL_BOT_TOKENS if BOT_TOKENS unset
- Config exposes botTokens: string[] instead of botToken + additionalBotTokens
- Updated env.ts, bot-pool.ts, docker-compose.yml, .env.example, CLAUDE.md, all tests

Speed audit (S3 -> Telegram upload flow):
- Hoisted 5 dynamic await import('../../../db/index') to top-level static imports
  in s3-controller.ts (3x) and web-api-controller.ts (2x)
  -> saves module resolution + async overhead on every upload
- Removed stale UPLOAD_CONCURRENCY env from docker-compose.yml
  (already removed from env.ts in prior refactor)

Upload flow is already concurrent:
- streamBodyToTemp() uses Bun.file(path).writer() — O(1) memory, safe for multi-GB blobs
- utils/chunked-storage.ts reads chunks serially but uploads concurrently with
  inFlight backpressure at effectiveConcurrency * 2 (= 16 with 8 bots)
- bot-pool.ts: per-bot PQueue(concurrency=1), 8 bots = 8 concurrent uploads per file,
  selectBot() picks least-loaded, 429 detection + inner+outer retry loops
- TELEGRAM_API_TIMEOUT_MS=120s — ample for 48MB chunks
- Infrastructure chunked-storage.ts (DI-based, dead code) has serial upload trap —
  noted for future cleanup

test/telegram.test.ts

@@ -148,7 +148,7 @@ describe('Telegram API Utilities', () => {
         file_size: 98765,
         mime_type: 'image/jpeg',
         file_path: 'photos/file_0.jpg',
-        bot_token: config.botToken,
+        bot_token: config.botTokens[0],
       });
     });
   });