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.

apps/desktop/pubspec.lock

@@ -608,6 +608,46 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.0.6"
+  screen_retriever:
+    dependency: transitive
+    description:
+      name: screen_retriever
+      sha256: ace919117a7520c13a50a6259e60c4a0d4cbe98809468792a91b5c5adada2aa6
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
+  screen_retriever_linux:
+    dependency: transitive
+    description:
+      name: screen_retriever_linux
+      sha256: "7b52006a5ceae1f3d5af7f77188c3290d6e7d8ded16d99809bea84967c65c257"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
+  screen_retriever_macos:
+    dependency: transitive
+    description:
+      name: screen_retriever_macos
+      sha256: a1489b99cce597c45a54b9aae1cd94c8d4705353b7e0bb2457a6e4de44e0ad8a
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
+  screen_retriever_platform_interface:
+    dependency: transitive
+    description:
+      name: screen_retriever_platform_interface
+      sha256: "94a5535277510a63184ca178ce12a1449bc0b38618879aa1c18bf57369c5064a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
+  screen_retriever_windows:
+    dependency: transitive
+    description:
+      name: screen_retriever_windows
+      sha256: dafc6922b0bfbf1d48cf3ccbf519b4fff47bdcb820da1728ea6db675fecc9324
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
   signals:
     dependency: "direct main"
     description:
@@ -811,6 +851,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.4.0"
+  window_manager:
+    dependency: "direct main"
+    description:
+      name: window_manager
+      sha256: "05c231fd7b23d2380f14c5cc10b7b93d60d4fa4a2fb4e0f032de27e44b5560e9"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.5.2"
   windows_file_picker:
     dependency: transitive
     description:
@@ -844,5 +892,5 @@ packages:
     source: hosted
     version: "3.1.4"
 sdks:
-  dart: ">=3.14.0-0 <4.0.0"
+  dart: ">=3.13.0-0 <4.0.0"
   flutter: ">=3.44.0"