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-transport/src/quic.rs

@@ -143,7 +143,7 @@ impl MediaTransport for QuinnTransport {
             }
         };
 
-        match datagram::deserialize_media(data) {
+        match datagram::deserialize_media(data.clone()) {
             Some(packet) => {
                 // Record receive observation
                 {
@@ -156,8 +156,10 @@ impl MediaTransport for QuinnTransport {
                 Ok(Some(packet))
             }
             None => {
-                tracing::warn!("received malformed media datagram");
-                Ok(None)
+                tracing::warn!(len = data.len(), "skipping malformed media datagram, continuing");
+                // Don't return Ok(None) — that signals connection closed.
+                // Recurse to read the next datagram instead.
+                Box::pin(self.recv_media()).await
             }
         }
     }