fix: live audio playback working — jitter buffer and decode loop fixes

- Reduced jitter buffer min_depth from 25 (500ms) to 3 (60ms) for fast start
- Fixed live recv loop: decode once per source packet instead of draining
  the jitter buffer dry (which advanced seq past future packets)
- Fixed Ok(None) handling: connection closed, not "no packet yet"

Live echo test confirmed working with continuous audio.

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

crates/wzp-client/src/call.rs

@@ -30,9 +30,9 @@ impl Default for CallConfig {
     fn default() -> Self {
         Self {
             profile: QualityProfile::GOOD,
-            jitter_target: 50,
+            jitter_target: 10,
             jitter_max: 250,
-            jitter_min: 25,
+            jitter_min: 3, // 60ms — low latency start, still smooths jitter
         }
     }
 }