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>

clients/android/native/src/decode.rs

@@ -161,7 +161,7 @@ fn run_sync(
         return;
     }
     log::info!(
-        "decode: HEVC decoder started at {}x{}",
+        "decode: {mime} decoder started at {}x{}",
         mode.width,
         mode.height
     );
@@ -815,7 +815,11 @@ fn run_async(
             })),
             on_error: Some(Box::new(move |e, code, _detail| {
                 let fatal = !code.is_recoverable() && !code.is_transient();
-                log::warn!("decode: codec error {e:?} (fatal={fatal})");
+                if fatal {
+                    log::error!("decode: fatal codec error — stream will stop: {e:?}");
+                } else {
+                    log::warn!("decode: codec error {e:?} (recoverable)");
+                }
                 let _ = err_tx.send(DecodeEvent::Error { fatal });
             })),
         };