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/punktfunk-host/src/windows/ddc.rs

@@ -181,9 +181,9 @@ pub fn panel_off_except(exclude_gdi: &str) -> u32 {
         acked += set_power(m.hmon, &m.device, POWER_OFF);
     }
     if acked == 0 {
-        tracing::info!(
-            "DDC/CI: no panel accepted the off command — the experiment is a no-op on this box \
-             (monitors without DDC/CI, or none besides the virtual display)"
+        tracing::debug!(
+            "DDC/CI: no physical panel accepted the DPMS-off command \
+             (no DDC/CI-capable panel besides the virtual display)"
         );
     }
     acked