FN-6516: preserve tablet chat sidebar width during typing

Keep tablet chat sidebars visible at the persisted width while the software keyboard is open.

- Preserve the non-mobile sidebar inline width instead of forcing tablet keyboard sessions to the minimum width.\n- Extend ChatView tablet viewport tests for default, persisted custom, and collapsed-sidebar keyboard states.\n- Document the FN-6516 refinement in the tablet keyboard viewport solution note.\n\nFiles changed:\n .../ui-bugs/tablet-keyboard-viewport-mode-flip.md  |  2 +\n packages/dashboard/app/components/ChatView.tsx     |  9 ++--\n .../__tests__/ChatView.mobile-render.test.tsx      | 55 ++++++++++++++++++----\n 3 files changed, 53 insertions(+), 13 deletions(-)

Fusion-Task-Id: FN-6516

Fusion-Task-Lineage: 51927ebb-3a9e-4dc5-827a-33c76a142335

docs/solutions/ui-bugs/tablet-keyboard-viewport-mode-flip.md

@@ -44,6 +44,8 @@ This preserves landscape-phone behavior while preventing keyboard-driven height
 
 ChatView also keeps a defense-in-depth CSS guard from FN-6210: `.chat-sidebar` has a non-mobile `max-width` matching `CHAT_SIDEBAR_MAX_WIDTH`, with the mobile media rule overriding it back to `100%`. That guard bounds the sidebar even if viewport-mode state is temporarily wrong and the inline sidebar width is removed.
 
+FN-6516 refined the FN-6494 keyboard-open behavior: tablet chat sidebars remain visible at the user's current/persisted width while the software keyboard is open, rather than narrowing to the minimum width. Resize controls still stay disabled while typing, collapsed sidebars remain collapsed, and the FN-6210 `max-width` CSS guard remains the upper bound.
+
 ## Regression coverage
 
 Cover the invariant rather than the single repro: