Session 48: Wire format design and logging improvements

Wire format:
- Add HandshakeMessageType enum (NoiseIKMsg1=0x01, NoiseIKMsg2=0x02)
- Define unified TLV framing for handshake and post-handshake messages
- Update fips-design.md and fips-protocol-flow.md with wire format details

Initialization:
- Defer TUN setup until after peer connections initiated
- Order: packet channel → transports → peers → TUN

Logging cleanup:
- Consolidate node/TUN info logs into aligned multi-line format
- TUN shutdown: single start/stop message, remove intermediate noise
- Remove ip link show callout and redundant Starting node message
- Change UDP transport stopped to debug level

src/lib.rs

@@ -41,9 +41,9 @@ pub use transport::udp::UdpTransport;
 
 // Re-export protocol types
 pub use protocol::{
-    CoordsRequired, DataFlags, DataPacket, FilterAnnounce, LinkMessageType, LookupRequest,
-    LookupResponse, PathBroken, ProtocolError, SessionAck, SessionDatagram, SessionFlags,
-    SessionMessageType, SessionSetup, TreeAnnounce,
+    CoordsRequired, DataFlags, DataPacket, FilterAnnounce, HandshakeMessageType, LinkMessageType,
+    LookupRequest, LookupResponse, PathBroken, ProtocolError, SessionAck, SessionDatagram,
+    SessionFlags, SessionMessageType, SessionSetup, TreeAnnounce,
 };
 
 // Re-export cache types