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-proto/src/codec_id.rs

@@ -105,10 +105,10 @@ pub struct QualityProfile {
 }
 
 impl QualityProfile {
-    /// Good conditions: Opus 24kbps, light FEC.
+    /// Good conditions: Opus 24kbps, FEC disabled for federation debugging.
     pub const GOOD: Self = Self {
         codec: CodecId::Opus24k,
-        fec_ratio: 0.2,
+        fec_ratio: 0.0,
         frame_duration_ms: 20,
         frames_per_block: 5,
     };