feat: add STARTTLS support for SMTP proxy server (#876)

* feat: add STARTTLS support for SMTP proxy server

Add smtp_tls_cert and smtp_tls_key environment variables to enable
STARTTLS on the SMTP proxy server, matching existing IMAP TLS support.

Closes #249

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add E2E tests for SMTP/IMAP STARTTLS

- Add smtp-proxy-tls service with self-signed certs in docker-compose
- Add smtp-tls.spec.ts: SMTP STARTTLS send plain/HTML/auth tests
- Add imap-tls.spec.ts: IMAP STARTTLS login/list/select/fetch tests
- Register smtp-proxy project in playwright.config.ts
- Wait for TLS proxy readiness in docker-entrypoint.sh

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: enforce auth over TLS when STARTTLS is configured

- Set auth_require_tls conditionally based on tls_context presence
- Disable insecure SSLv2/SSLv3 protocols in TLS context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: replace cert-gen service with inline cert generation

The cert-gen one-shot container was exiting immediately after
generating certificates, triggering --abort-on-container-exit
and stopping all services before tests could run.

Replace with an entrypoint script in smtp-proxy-tls that generates
the self-signed cert before starting the proxy server.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

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

e2e/docker-compose.yml

@@ -45,6 +45,28 @@ services:
       worker:
         condition: service_healthy
 
+  smtp-proxy-tls:
+    build:
+      context: ../smtp_proxy_server
+      dockerfile: dockerfile
+    ports:
+      - "11026:8026"
+      - "11144:11144"
+    environment:
+      PROXY_URL: http://worker:8787
+      PORT: "8026"
+      IMAP_PORT: "11144"
+      smtp_tls_cert: /certs/cert.pem
+      smtp_tls_key: /certs/key.pem
+      imap_tls_cert: /certs/cert.pem
+      imap_tls_key: /certs/key.pem
+    entrypoint: ["/bin/bash", "/e2e-scripts/smtp-tls-entrypoint.sh"]
+    volumes:
+      - ./scripts:/e2e-scripts:ro
+    depends_on:
+      worker:
+        condition: service_healthy
+
   e2e-runner:
     build:
       context: ..
@@ -54,7 +76,11 @@ services:
       FRONTEND_URL: http://frontend:5173
       MAILPIT_API: http://mailpit:8025/api
       SMTP_PROXY_HOST: smtp-proxy
+      SMTP_PROXY_SMTP_PORT: "8025"
       SMTP_PROXY_IMAP_PORT: "11143"
+      SMTP_PROXY_TLS_HOST: smtp-proxy-tls
+      SMTP_PROXY_TLS_SMTP_PORT: "8026"
+      SMTP_PROXY_TLS_IMAP_PORT: "11144"
       CI: "true"
     depends_on:
       worker:
@@ -63,6 +89,8 @@ services:
         condition: service_started
       smtp-proxy:
         condition: service_started
+      smtp-proxy-tls:
+        condition: service_started
     volumes:
       - ./test-results:/app/e2e/test-results
       - ./playwright-report:/app/e2e/playwright-report