cache the kernel ref so dispose() can actually clean up (T-366)

ClideKernel.of(context) is an illegal ancestor lookup inside
dispose(); both panes wrapped it in catch (_) and silently did
nothing. The terminal pane therefore never sent pane.close (backend
PTY + daemon pane leaked per closed pane) and the Claude pane never
removed its settings listener. Both now cache KernelServices in
didChangeDependencies and the swallow-everything helpers are gone.
New terminal_pane_test covers the close-on-dispose path; note in it
why the whole tree must unmount (harness Overlay keeps
initialEntries across rebuilds).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -36,6 +36,11 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
   terminal or Claude pane whose process ended naturally left its pty device
   open for the life of the app; natural exit now releases the fd. (T-360)
 
+- **Closing a terminal pane now closes its shell.** Pane disposal looked up
+  the kernel illegally and swallowed the failure, so `pane.close` was never
+  sent — the backend PTY and daemon pane leaked on every closed terminal
+  pane, and Claude panes leaked a settings listener the same way. (T-366)
+
 - **Accepting ExitPlanMode now leaves plan mode in the conversation panel.**
   Approving Claude's plan (the ExitPlanMode tool) transitioned the underlying
   session out of plan mode, but clide's tracked permission mode didn't follow,