fix: rewrite seq/fec for federation-delivered packets

- Time-based dedup (2s TTL) replaces fixed-window dedup — consecutive
  senders with same seq numbers no longer collide
- Raw byte forwarding for federation local delivery (no re-serialization)
- Jitter buffer resets on large backward seq jumps (>100)
- recv_media skips malformed datagrams instead of returning connection-closed
- SIGTERM handler for clean QUIC shutdown on wzp-client
- JSONL event log infrastructure (--event-log flag) for protocol analysis
- FEC disabled on GOOD profile for federation debugging (fec_ratio=0.0)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-relay/src/lib.rs

@@ -9,6 +9,7 @@
 
 pub mod auth;
 pub mod config;
+pub mod event_log;
 pub mod federation;
 pub mod handshake;
 pub mod metrics;