feat: add TLS support to Rust implementation

- Add async-native-tls dependency for secure IMAP connections
- Implement ImapStream enum supporting both TLS and plain connections
- Add automatic TLS detection based on port (993=TLS, 143=plain, 3143=test)
- Add comprehensive Read/Write trait implementations for stream wrapper
- Add debug logging for connection type verification
- Create example configurations for Gmail, Outlook, and other providers
- Add TLS_SUPPORT.md documentation with security guidelines
- Test with existing test environment and TLS detection logic
- Maintain backward compatibility with plain IMAP for testing

The Rust implementation now supports secure connections to production
email providers while maintaining compatibility with test environments.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

rust/config-gmail-example.json

@@ -0,0 +1,26 @@
+{
+  "couchDb": {
+    "url": "http://localhost:5984",
+    "user": "admin",
+    "password": "password"
+  },
+  "mailSources": [
+    {
+      "name": "Personal Gmail",
+      "enabled": true,
+      "protocol": "imap",
+      "host": "imap.gmail.com",
+      "port": 993,
+      "user": "your-email@gmail.com",
+      "password": "your-app-password",
+      "mode": "archive",
+      "folderFilter": {
+        "include": ["INBOX", "[Gmail]/Sent Mail"],
+        "exclude": ["[Gmail]/Trash", "[Gmail]/Spam"]
+      },
+      "messageFilter": {
+        "since": "2024-01-01"
+      }
+    }
+  ]
+}