refactor: modularize IMAP server with dual login, STARTTLS, and test suite (#859)

refactor: modularize IMAP server with fixes and E2E tests

- Modularize IMAP server into imap_server, imap_mailbox, imap_message,
  imap_http_client, parse_email, config, models
- Support dual login: JWT token and address+password via backend
- Add STARTTLS support with configurable TLS cert/key
- Fix FETCH/STORE returning UID instead of sequence number (RFC 3501)
- Implement IMessageFile.open() for correct BODY[] raw MIME delivery
- Add UIDNEXT to SELECT response via _cbSelectWork override
- Use per-restart UIDVALIDITY to force client resync
- Pass raw MIME to SimpleMessage for accurate RFC822.SIZE
- Fix SENT mailbox returning empty source
- Handle CREATE command gracefully for Thunderbird compatibility
- Add IMAP E2E tests: auth, LIST, SELECT, STATUS, FETCH, SEARCH,
  STORE, UID FETCH, BODY[] integrity, size, seq numbers, SENT mailbox
- Add SMTP E2E tests using nodemailer: send plain/HTML, auth failure,
  sendbox verification
- Add sendTestMail helper using admin/send_mail

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

e2e/docker-compose.yml

@@ -30,6 +30,21 @@ services:
       worker:
         condition: service_healthy
 
+  smtp-proxy:
+    build:
+      context: ../smtp_proxy_server
+      dockerfile: dockerfile
+    ports:
+      - "11025:8025"
+      - "11143:11143"
+    environment:
+      PROXY_URL: http://worker:8787
+      PORT: "8025"
+      IMAP_PORT: "11143"
+    depends_on:
+      worker:
+        condition: service_healthy
+
   e2e-runner:
     build:
       context: ..
@@ -38,12 +53,16 @@ services:
       WORKER_URL: http://worker:8787
       FRONTEND_URL: http://frontend:5173
       MAILPIT_API: http://mailpit:8025/api
+      SMTP_PROXY_HOST: smtp-proxy
+      SMTP_PROXY_IMAP_PORT: "11143"
       CI: "true"
     depends_on:
       worker:
         condition: service_healthy
       frontend:
         condition: service_started
+      smtp-proxy:
+        condition: service_started
     volumes:
       - ./test-results:/app/e2e/test-results
       - ./playwright-report:/app/e2e/playwright-report