chore: consolidate parallel-session WIP (HOLD — do not push)

Local snapshot of intermingled in-flight work, committed to unblock the encode
refactor (a clean ffmpeg_win.rs for the vbv-dedup follow-on). These hunks span
the same files and can't be cleanly split here; the commit bundles three
distinct workstreams that each belong in their own PR:

  - logging rework (~43 files: level re-tiering, structured fields, `?e`,
    hot-path flood latches)
  - conflicting-host detection (detect.rs + detect/{linux,windows}.rs + wiring
    in main.rs/mgmt.rs/Cargo.toml/docs/packaging)
  - standby-sink DWM-stall attribution (windows/display_events.rs + capture/
    vdisplay wiring)

NOT verified as a combination. NOT to be pushed until the refactor is done and
these are re-verified and reorganized into their proper per-workstream PRs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-client-core/src/video.rs

@@ -510,7 +510,7 @@ impl Decoder {
                     if choice == "vaapi" {
                         return Err(e.context("PUNKTFUNK_DECODER=vaapi but VAAPI failed"));
                     }
-                    tracing::info!(reason = %e, "VAAPI unavailable — software decode");
+                    tracing::warn!(error = %e, "VAAPI unavailable — falling back to software decode");
                 }
             }
         }
@@ -695,8 +695,8 @@ impl Decoder {
                     self.backend = Backend::Software(SoftwareDecoder::new(self.codec_id)?);
                     self.vaapi_fails = 0;
                 } else {
-                    tracing::warn!(error = %e,
-                        "{which} decode error — requesting keyframe, keeping hardware decode");
+                    tracing::debug!(backend = which, error = %e,
+                        "decode error — requesting keyframe, keeping hardware decode");
                 }
                 Ok(None)
             }
@@ -1653,7 +1653,7 @@ unsafe extern "C" fn pick_vulkan(
             &mut fr,
         );
         if r < 0 || fr.is_null() {
-            tracing::warn!("avcodec_get_hw_frames_parameters(VULKAN) failed ({r})");
+            tracing::warn!(code = r, "avcodec_get_hw_frames_parameters(VULKAN) failed");
             return ffi::AVPixelFormat::AV_PIX_FMT_NONE;
         }
         let fc = (*fr).data as *mut ffi::AVHWFramesContext;
@@ -1665,7 +1665,7 @@ unsafe extern "C" fn pick_vulkan(
             as _;
         let r = ffi::av_hwframe_ctx_init(fr);
         if r < 0 {
-            tracing::warn!("av_hwframe_ctx_init(VULKAN) failed ({r})");
+            tracing::warn!(code = r, "av_hwframe_ctx_init(VULKAN) failed");
             let mut fr = fr;
             ffi::av_buffer_unref(&mut fr);
             return ffi::AVPixelFormat::AV_PIX_FMT_NONE;