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/PROTOCOL.md

@@ -45,6 +45,10 @@ force-hold, kick, join, leave, stale, swap, seek, pause, resume, chat —
 every one carries actor + server timestamp.
 Force-play-all is `force` with `target:"all",ready:true`; anyone not
 ready Spaces back. Sounds key off feed actions.
+Chat dual delivery: the server emits both `{"t":"chat","text","from"}`
+(render this one — it carries the text) and a textless `feed` chat
+entry (housekeeping echo). Clients must render exactly one row per
+send; the reference client drops the textless feed entry.
 
 ## Membership set (kills join-cascade + ghost-quorum)