reveal non-Claude workspace tabs in a split above Claude

A live test of ui open diff surfaced that the workspace slot hardcoded
the Claude pane (primary = claude ?? active), so activating diff.view
flipped the registry but never rendered. Generalise _WorkspaceSlot: when
a non-Claude, non-editor workspace tab is the active one, reveal it in
the split region above Claude with a close affordance back to full-Claude
— so clide ui open diff actually shows the diff alongside the
conversation. Fixes the reveal for terminal/team-chat tabs too.

Closes T-233.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,8 +18,10 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
-- `clide ui open diff <path>` reveals the diff tab and scrolls to that file's
-  diff, highlighting its header — the diff-panel arm of `ui open` (T-233).
+- `clide ui open diff <path>` reveals the diff in a split above the Claude
+  conversation, scrolls to that file and highlights its header — the
+  diff-panel arm of `ui open`. Workspace tabs other than Claude/editor now
+  reveal alongside the conversation with a close affordance (T-233).
 - Image cards in the Claude conversation log: `clide image show <path>
   [--caption …]` renders an image inline (PNG/JPG/JPEG/GIF/WebP/BMP),
   clide-owned and display-only (D-78). The path is resolved workspace-relative