fix: mic mute crackling + add AEC/NoiseSuppressor + dedup room participants

Mic mute: the send loop now zeros the capture buffer when muted instead
of relying on write_audio() to skip writes. Previously stale ring data
and AGC amplification of near-silence caused crackling artifacts.

AEC: attach Android's hardware AcousticEchoCanceler to the AudioRecord
session. Also attach NoiseSuppressor when available. Both are released
on capture stop.

Room UI: deduplicate participants by fingerprint so ghost entries from
stale relay state don't show duplicate names.

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

crates/wzp-android/src/engine.rs

@@ -339,6 +339,12 @@ async fn run_call(
                 continue;
             }
 
+            // Mute: zero out the buffer so Opus encodes silence.
+            // We still read from the ring to prevent it from filling up.
+            if state.muted.load(Ordering::Relaxed) {
+                capture_buf.fill(0);
+            }
+
             // AGC: normalize capture volume before encoding
             capture_agc.process_frame(&mut capture_buf);