feat(portal): BWE-driven resolution adaptation + duplicate frame skipping

WebRTC client bandwidth estimate now drives both encoder bitrate and
resolution tier selection, replacing the previous static-target encoder.

- webrtc.rs: enable str0m BWE (seeded at 5 Mbps), surface
  EgressBitrateEstimate + KeyframeRequest events, expose
  get_bwe_estimate() / set_need_keyframe()
- state_portal.rs: wire bitrate/resolution channels between the WebRTC
  thread and the encode thread; tier ladder [1440p, 1080p, 720p] with
  downscale at 60% budget and upscale hysteresis (120% sustained 10s)
- avhw.rs: SwEncImport::poll_resolution_commands() rebuilds the import
  filter graph on UpdateResolution; SwEncEncode::recreate_encoder()
  rebuilds sws/enc_video/yuv_frame atomically; hash_sampled_y_plane()
  skips duplicate frames; VBV x264opts cap IDR bursts; H.264 level 4.0
  (muxer) / 4.2 (WebRTC)
- state.rs: sync wlr-screencopy GOP to fps*2 max 20 for parity
- fix: drain bitrate_rx + resolution_rx BEFORE the stride check in
  encode_cpu_frame() so the new (smaller-stride) frame produced after
  a resolution change does not hit the stale (larger) enc_width and
  crash the encode thread
- WebRTC GOP widened to fps*2 max 20 (was fps/2 max 10)

src/main.rs

@@ -15,9 +15,9 @@ mod backend_detect; // 截屏后端自动检测（wlroots vs Portal/PipeWire）
 mod cap_portal; // XDG Portal 屏幕捕获
 mod cap_wlr_screencopy; // wlroots wlr-screencopy 截屏协议
 mod fps_limit; // 帧率限制器
-mod stats; // 管道性能统计（卡顿诊断）
 mod state; // wlr-screencopy 后端的主状态机
 mod state_portal; // Portal/PipeWire 后端的主状态机
+mod stats; // 管道性能统计（卡顿诊断）
 mod transform; // 图像变换（旋转/翻转）
 mod webrtc; // WebRTC 传输（str0m Sans-IO）
 
@@ -46,21 +46,27 @@ fn main() -> Result<()> {
 
     // 根据 verbose 模式或 RUST_LOG 环境变量设置日志级别
     // 支持 RUST_LOG 粒度控制（如 RUST_LOG=wl_webrtc::webrtc=trace）
-    let env_filter = tracing_subscriber::EnvFilter::try_from_default_env()
-        .unwrap_or_else(|_| {
-            if args.verbose {
-                tracing_subscriber::EnvFilter::new("debug")
-            } else {
-                tracing_subscriber::EnvFilter::new("info")
-            }
-        });
+    let env_filter = tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| {
+        if args.verbose {
+            tracing_subscriber::EnvFilter::new("debug")
+        } else {
+            tracing_subscriber::EnvFilter::new("info")
+        }
+    });
     tracing_subscriber::fmt()
         .with_env_filter(env_filter)
         .with_writer(std::io::stderr)
         .init();
 
     tracing::info!("wl-webrtc starting");
-    tracing::debug!("Args: output={:?} fps={} codec={} port={} verbose={}", args.output, args.fps, args.codec, args.port, args.verbose);
+    tracing::debug!(
+        "Args: output={:?} fps={} codec={} port={} verbose={}",
+        args.output,
+        args.fps,
+        args.codec,
+        args.port,
+        args.verbose
+    );
 
     // MVP 阶段仅支持 H.264 编码，不支持 HEVC
     if args.codec != "h264" {
@@ -352,7 +358,9 @@ fn run_portal_pipewire(args: Args) -> Result<()> {
 
         // Portal 状态机遇到致命错误时退出
         if state.is_errored() {
-            tracing::error!("Fatal error in portal state machine (check preceding error logs), exiting");
+            tracing::error!(
+                "Fatal error in portal state machine (check preceding error logs), exiting"
+            );
             running = false;
         }
     }