feat: desktop GUI enhancements — audio level, call timer, VPIO, settings

- Audio level meter with log-scale RMS visualization
- Call duration timer
- VPIO (OS AEC) wired through to engine with fallback to CPAL
- "You" badge on own participant entry
- Recent rooms list (click to reuse)
- Enter key to connect from form fields
- Improved dark theme with pulse animation on status dot
- Settings persistence via localStorage (relay, room, alias, AEC, recent rooms)
- Fingerprint display on connect screen
- Keyboard shortcuts skip input fields

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

desktop/src-tauri/Cargo.toml

@@ -25,7 +25,7 @@ wzp-codec = { path = "../../crates/wzp-codec" }
 wzp-fec = { path = "../../crates/wzp-fec" }
 wzp-crypto = { path = "../../crates/wzp-crypto" }
 wzp-transport = { path = "../../crates/wzp-transport" }
-wzp-client = { path = "../../crates/wzp-client", features = ["audio"] }
+wzp-client = { path = "../../crates/wzp-client", features = ["audio", "vpio"] }
 
 # Platform-specific
 [target.'cfg(target_os = "macos")'.dependencies]