feat(gui): one-click Close in its own bottom sidebar section

Close is now a direct shutdown trigger: visiting the Close page (the
sidebar entry) fires shutdown_app() immediately — no confirm step, no
intermediate body. The farewell overlay paints and os._exit(0) lands
~1s later from a daemon thread.

Layout: Close moved into its own bottom-of-sidebar section so the
destructive action is visually separated from Account/Activate.

- New shutdown_app() in components/_legacy.py replaces quit_button.
  os._exit thread is skipped when "pytest" is in sys.modules so the
  test suite doesn't suicide on rendering 99_Close.
- pages/99_Close.py shrinks to set_page_config + chrome + shutdown_app.
- app.py nav grows a new "Close" section header (new
  nav.section_close key in en/es packs) pinned at the bottom of the
  navigation dict.

Tests updated:
- TestQuitButtonRenders → TestClosePageShutsDownImmediately.
  Assert the shutdown caption renders + no confirm button exists.
- test_smoke EXPECTED_SUBSTRINGS["99_Close"] now pins
  "Shutting down" / "Cerrando" (the visible page body) instead of
  the removed page title.

2008 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/gui/components/_legacy.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import io
 import os
+import sys
 import threading
 import time
 from typing import Optional
@@ -186,37 +187,38 @@ def _farewell_script() -> str:
     )
 
 
-def quit_button(label: str | None = None, *, key: str = "quit_app_button") -> None:
-    """Render a Quit button that terminates the Streamlit server.
+def shutdown_app() -> None:
+    """Terminate the Streamlit server immediately, no confirm.
+
+    Designed to be called from a page whose mere act of rendering means
+    the user wants to quit (e.g., the sidebar Close entry). Schedules
+    ``os._exit(0)`` on a daemon thread so the process terminates after
+    the farewell overlay has had a chance to paint, then injects the
+    overlay JS and short-circuits the rest of the page via ``st.stop``.
 
     Streamlit has no first-class shutdown hook, and signalling the
     process (SIGTERM/SIGINT) does not reliably terminate it — Streamlit
     installs its own handlers and the tornado/asyncio loop swallows or
     defers the signal, so the browser sees the websocket drop while the
-    python process stays alive. We schedule ``os._exit(0)`` on a daemon
-    thread to hard-kill the process, and inject a small JS shim that
-    either closes the tab (when allowed) or replaces the top frame with
-    a self-contained "App closed" page so the user never sees
-    Streamlit's red connection-error overlay.
+    python process stays alive. ``os._exit`` is the only reliable kill.
+
+    The hard-exit thread is skipped under pytest so the test suite does
+    not suicide when a test renders this page. The overlay + caption
+    still render so test assertions about content work.
     """
-    if label is None:
-        label = _t("quit.button")
-
-    if st.session_state.get("_app_shutting_down"):
-        from streamlit.components.v1 import html as _components_html
-        _components_html(_farewell_script(), height=0)
-        st.success(_t("quit.shutting_down"))
-        st.stop()
-
-    if st.button(label, key=key, type="secondary"):
+    if not st.session_state.get("_app_shutting_down"):
         st.session_state["_app_shutting_down"] = True
+        if "pytest" not in sys.modules:
+            def _hard_exit() -> None:
+                time.sleep(1.0)
+                os._exit(0)
 
-        def _hard_exit() -> None:
-            time.sleep(1.0)
-            os._exit(0)
+            threading.Thread(target=_hard_exit, daemon=True).start()
 
-        threading.Thread(target=_hard_exit, daemon=True).start()
-        st.rerun()
+    from streamlit.components.v1 import html as _components_html
+    _components_html(_farewell_script(), height=0)
+    st.success(_t("quit.shutting_down"))
+    st.stop()
 
 
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