Implement manual TLS certificate loading and ServerConfig construction

- Add tls::config module with manual TLS mode support
- Load PEM certificates and private keys via rustls_pemfile
- Build ServerConfig with aws_lc_rs crypto provider
- Restrict cipher suites per ADR-012 (4 TLS 1.2 ECDHE-AES-GCM + all TLS 1.3)
- Configure protocol versions to TLS 1.2 and 1.3 only
- Implement SniCertResolver for multi-domain manual mode
- Unknown SNI hostname fails handshake (no default cert)
- Add tempfile dev dependency for test file operations
- Add 11 unit tests covering config, cipher suites, and SNI resolution

Cargo.toml

@@ -34,4 +34,5 @@ thiserror = "=2.0.18"
 
 [dev-dependencies]
 rcgen = "=0.13"
-reqwest = { version = "=0.12", features = ["json"] }
+reqwest = { version = "=0.12", features = ["json"] }
+tempfile = "=3.20"