Add Security Audit Phase 9: comprehensive SSH security tests

- auth_security: password brute force, public key, user status, home dir
- crypto_security: AES-CTR, HMAC-SHA256, Curve25519, Ed25519
- file_access_security: path traversal, absolute path, symlink attack
- channel_security: window limits, request validation
- 18 new security tests, all pass (153 total)

markbase-core/src/provider/mod.rs

@@ -1,6 +1,9 @@
 pub mod sqlite;
 pub mod pg;
 
+pub use sqlite::SqliteProvider;
+pub use pg::PgProvider;
+
 use std::path::PathBuf;
 
 /// 用户信息