feat(app): discoverable restore affordance when Chat is collapsed (#1434) #1611

Important

Problem — When the Chat is collapsed, the only way to restore it is a small chevron button at the left edge or pressing Cmd+Shift+M. The chevron is easy to miss and doesn't communicate what it does. Users get stuck in maximized mode.

Approach — Replace the thin chevron with a VS Code-style restore affordance: a narrow vertical strip (8-12px wide) on the left edge of the Work Column that shows a subtle hover state (background highlight + expand icon). Clicking it restores the Chat. The strip is always visible when Chat is collapsed — not just on hover — so the user always sees the way back. A tooltip on hover says "Show Chat (⌘⇧M)".

Approaches considered — (A) Thin always-visible strip with hover highlight (VS Code pattern) — chosen; discoverable without cluttering the UI. (B) Floating pill/badge — more discoverable but takes content space. (C) Only the keyboard shortcut — not discoverable.

Scope — In: left-edge restore strip, hover highlight, tooltip, click-to-restore. Out: drag-to-restore (that's the resize handle's job), animation (separate issue).