T5.1: PriorityMode enum + SetPriorityMode signal; extend QualityProfile with video fields

crates/wzp-proto/src/priority_mode.rs

@@ -0,0 +1,24 @@
+//! Priority mode for bandwidth allocation between audio and video.
+//!
+//! See `docs/PRD/PRD-video-quality-priority.md` for the full design.
+
+use serde::{Deserialize, Serialize};
+
+/// Bandwidth-allocation policy between audio and video.
+///
+/// Carried on [`QualityProfile`](crate::QualityProfile) and mutable at
+/// runtime via [`SignalMessage::SetPriorityMode`](crate::SignalMessage).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
+pub enum PriorityMode {
+    /// Audio gets its floor first; video gets the remainder.
+    /// Default for voice/video calls.
+    #[default]
+    AudioFirst,
+    /// Video gets its floor first; audio degrades to Opus 16k floor.
+    VideoFirst,
+    /// Audio clamped to 16 kbps (intelligible speech); video gets remainder.
+    /// Falls back to slide mode when bandwidth drops below SD floor.
+    ScreenShare,
+    /// Proportional split (~15 % audio, ~85 % video).
+    Balanced,
+}