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/env.test.ts

@@ -3,7 +3,7 @@ import { config } from '../src/env';
 
 describe('Environment Variables Validation', () => {
   it('config should have all required fields', () => {
-    expect(config).toHaveProperty('botToken');
+    expect(config).toHaveProperty('botTokens');
     expect(config).toHaveProperty('storageChatId');
     expect(config).toHaveProperty('baseUrl');
     expect(config).toHaveProperty('databaseUrl');
@@ -17,8 +17,9 @@ describe('Environment Variables Validation', () => {
     expect(config).toHaveProperty('sessionMaxAgeMs');
   });
 
-  it('config.botToken should return BOT_TOKEN from process.env', () => {
-    expect(config.botToken).toBe(process.env.BOT_TOKEN || '');
+  it('config.botTokens should return array from BOT_TOKENS env', () => {
+    expect(Array.isArray(config.botTokens)).toBe(true);
+    expect(config.botTokens.length).toBeGreaterThanOrEqual(3);
   });
 
   it('config.storageChatId should be parsed as integer from STORAGE_CHANNEL_ID', () => {
@@ -52,10 +53,10 @@ describe('Environment Variables Validation', () => {
     expect(config.sessionMaxAgeMs).toBe(86400 * 1000);
   });
 
-  it('additionalBotTokens should be populated in test environment', () => {
-    expect(Array.isArray(config.additionalBotTokens)).toBe(true);
-    // With mock tokens from setup-env.ts there should be 2 additional tokens
-    expect(config.additionalBotTokens.length).toBeGreaterThanOrEqual(2);
+  it('botTokens should be populated in test environment', () => {
+    expect(Array.isArray(config.botTokens)).toBe(true);
+    // With mock tokens from setup-env.ts there should be at least 3 tokens
+    expect(config.botTokens.length).toBeGreaterThanOrEqual(3);
   });
 
   it('S3 validation should not throw — env already loaded without error at import time', () => {