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/config.rs

@@ -90,6 +90,9 @@ pub struct RelayConfig {
     /// Debug tap: log packet headers for matching rooms ("*" = all rooms).
     /// Activated via --debug-tap <room> or debug_tap = "room" in TOML.
     pub debug_tap: Option<String>,
+    /// JSONL event log path for protocol analysis (--event-log).
+    #[serde(skip)]
+    pub event_log: Option<String>,
 }
 
 impl Default for RelayConfig {
@@ -112,6 +115,7 @@ impl Default for RelayConfig {
             global_rooms: Vec::new(),
             trusted: Vec::new(),
             debug_tap: None,
+            event_log: None,
         }
     }
 }