[FEATURE] VS Code extension: option to keep session tiles at a fixed size in the multi-session grid

Problem

In the VS Code extension, when multiple sessions are shown side by side as a grid of tiles, clicking a session tile expands it (the focused session gets a larger area and other tiles shrink/rearrange).

When monitoring several sessions in parallel, I want all tiles to stay the same size so I can see every session at a glance, even while typing into one of them.

Proposed solution

Add a setting (or a toggle in the grid UI) to disable expand-on-focus, so that the grid keeps uniform tile sizes when a session is clicked/focused.

Current workaround

Pressing Esc after interacting with a session returns the grid to uniform sizes, but the layout jumps every time a session is clicked.