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-presenter/src/dmabuf.rs

@@ -101,7 +101,7 @@ pub fn import(
     // EGL could leave an INVALID modifier to the driver's implied choice; explicit-
     // modifier images can't — LINEAR is the only honest guess (debug-visible if wrong).
     let modifier = if frame.modifier == DRM_FORMAT_MOD_INVALID {
-        tracing::debug!("dmabuf carried no explicit modifier — importing as LINEAR");
+        tracing::trace!("dmabuf carried no explicit modifier — importing as LINEAR");
         DRM_FORMAT_MOD_LINEAR
     } else {
         frame.modifier