fix(app-boot): keep the fail-loud exit fatal while the terminal is released

Review of the previous commit found two defects in the release path, both
reproduced against the implementation:

- The timeout guarding a never-settling release was unref'ed. An
  unhandledRejection listener suppresses Node's default fatal exit, so with
  nothing else referenced the process reached an empty event loop and exited
  0 on the very failure it was reporting. Keep the timer referenced and clear
  it once the race settles.

- The handler uninstalled itself before awaiting the release. A second
  concurrent rejection then became uncaught and killed the process
  mid-teardown, stranding exactly the terminal state this restores. Replace
  the uninstall with a latch: the first rejection is the reported one, and
  later rejections (teardown's own included) fall through to the pending exit.

Add the PTY regression the fake-process tests cannot express: boot the shipped
tree over a fixture whose llm-pi-ai providers value is list-shaped, expect exit
1, and assert the captured bytes carry both the diagnostic and ESC[?2004l.
Against the pre-fix source the stream ends at ESC[?2004h ESC[>7u ESC[?u ESC[c
with no reset and the case fails, so it pins the actual bug.

Split the two-shape formatting test into one install per case; a latched
handler reports once by design.

apps/cli/tests/fixtures/tui-invalid-provider.cordis.yml

@@ -0,0 +1,10 @@
+# An overlay whose `llm-pi-ai` config fails schema validation: `providers` is a
+# dict keyed by provider name, and a list is the shape users reach for. The
+# entry rejects while `ui-tui` — mounted concurrently by the Loader — already
+# holds the terminal, which is the boot failure the fail-loud release hook
+# exists for.
+- id: llm-pi-ai
+  config:
+    providers:
+      - provider: openai
+        apiKey: keyless-invalid-shape