Desktop session batch 09-12: frameless chrome, bisect removal, chat/idle fixes

Frameless (window_manager, hidden titlebar): chrome bar on welcome,
drag-to-move appbar + window buttons on connect, drag layer + window
buttons in session controls; min size 160x90; volume-scroll off for
drag; session maximize = fullscreen toggle. Verified on KDE Wayland.
Delete legacy/minimal/nosheet bisect screens; session routes direct
(black-screen fix verified incl. WAN).
Avatar: pipeline now 128px aspect-kept PNG (was cropped JPEG);
profile card centered 64px hover-to-change; member avatar drops
ResizeImage downscale. NOTE open: pipeline 512 KiB check vs server
64 KiB enforcement mismatch.
Fixes: idle warn/unready skipped while PLAYING; sendChat drops
blanks; one chat row per send (drop textless server feed echo);
chat field keeps focus after send. Playback libass true; sdk floor
3.13. Handoff 9-11: 9+10 fixed, 11 jumpy seek still open.
Docs: handoff/roadmap/protocol record all of the above; few-commits
preference going forward.

docs/ROADMAP.md

@@ -60,10 +60,9 @@ join/reject logs in `room_hub.dart`); Cancel aborts a pending
 connect (`SyncClient.disconnect` completes the welcome future);
 first-join failure shows the dialog and stops (auto-reconnect only
 after an established session drops).
-Open exits (manual, user-driven): remove bisect flags in
-`apps/desktop/lib/app.dart`; 2-client LAN soak; 1.4 GB real-file test
-(user resupplies URL, never paste api_key into files);
-cache-exhaustion long outage.
+Open exits (manual, user-driven): bisect flags REMOVED 09-12;
+2-client LAN soak + 1.4 GB real-file test user-reports-done 09-12
+(details pending). Still open: cache-exhaustion long outage.
 
 ## Phase 5 — Resilience (PARTIAL)