Add SSH config parser tests

[quiloos39]

Summary

• Add 16 tests for buildConnectConfig() and expandTilde() in src/config.ts
• Covers tilde expansion, default values (port 22, username, keepalive, readyTimeout), explicit parameter overrides, auth priority (password > key > agent), SSH agent fallback, and host resolution passthrough

Test plan

• Run node --import tsx --test tests/config-parser.test.ts and verify all 16 tests pass
• Verify auth priority matches documented order: explicit password > explicit key > SSH config IdentityFile > SSH agent