fix(workspaces): empty state + disabled input when workspace has no harness

[DIodide]

Summary

• When a workspace was selected with no harness attached, the chat page rendered the generic EmptyChat plus a fully interactive ChatInput whose handleSend silently no-oped — the user could type and click send with no feedback.
• Adds a dedicated NoHarnessAttachedState screen that names the active workspace and provides an "Attach a harness" CTA. The CTA opens the existing edit-workspace dialog (where the harness selector already lives) by plumbing a pendingEditWorkspaceId request through WorkspaceSidebar.
• Disables the chat input (textarea + send button) whenever !activeHarness, with a context-aware placeholder:
  • no workspace selected → "Select a workspace to start chatting"
  • workspace without harness → "Attach a harness to this workspace to start chatting"

Files

• apps/web/src/routes/workspaces/index.tsx
  • new NoHarnessAttachedState screen (mirrors the visual language of EmptyWorkspaceState, uses the Wrench icon)
  • new render branch: !activeWorkspace → EmptyWorkspaceState, !activeHarness → NoHarnessAttachedState, else conversation/empty-chat
  • ChatInput gains disabled and placeholder props; both wired into the textarea and send button
  • WorkspaceSidebar gains pendingEditWorkspaceId / onPendingEditConsumed props and a small effect that opens the rename dialog when triggered externally

Test plan

• Create a workspace with no harness attached, navigate to it
  • The center pane shows the new "No harness attached" screen with the workspace name
  • Clicking Attach a harness opens the sidebar (if collapsed) and the Edit Workspace dialog with the harness selector focused
  • The chat textarea is disabled and shows "Attach a harness to this workspace to start chatting"
  • The send button stays disabled even after typing (it shouldn't be possible to type, but the guard belt-and-suspenders)
• Attach a harness from the dialog → empty-chat + interactive input return as expected
• No regressions on workspaces that already have a harness
• No regression on the !activeWorkspace path (EmptyWorkspaceState still renders, input shows "Select a workspace to start chatting")