fix(workspace): stop layout jumps and stale chrome when switching workspaces

[juacker]

Problem

When you switched from workspace A to workspace B, the page kept showing A's data until B's details finished loading. That included A's header, drawer, counts and run state. So pressing Stop or Ctrl+C during that time could cancel A's run. The chat area's padding also animated on every switch.

Fix (src/pages/Workspace.tsx)

• The raw state is renamed to rawDetails. Every consumer now reads details, which is only set once it matches the current workspaceId, so everything is gated by default.
• While B loads, the header shows the sidebar title with title editing turned off, and the drawer shows "Loading…".
• Replies and updater writes that belong to a workspace you already left are dropped. They are checked at every await point, and a ref updated in a layout effect tracks the current workspace.
• The chat area is keyed by workspace, so its padding no longer animates on a switch.

Tests

Workspace.test.tsx covers:

• the Stop button and counts not showing A's run while B loads;
• the drawer and tasks/memories/artifactCount gates;
• the sidebar title shown while loading;
• A's late reply being dropped after switching to B.

Lint, typecheck and vitest (700 tests) pass locally.

Not covered

• The padding animation can't be tested in jsdom. It needs a check in the real app.
• Known follow-ups from review (minor): A's in-flight runNowBusy/pauseBusy flags and setError calls can still land on B, an existing error banner survives the switch, and the catch/finally guards have no test.