fix(gui): move Quit button to sidebar so it shows on every page

The footer placement was easy to miss (below all tool cards) and only
rendered on the home page. Hook the button into hide_streamlit_chrome()
so every page that hides default chrome — home + all 9 tool pages — gets
the Quit button at the bottom of the sidebar without per-page edits.

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

src/gui/app.py

@@ -24,7 +24,6 @@ if str(_project_root) not in sys.path:
 from src.gui.components import (
     findings_count_for_tool,
     hide_streamlit_chrome,
-    quit_button,
     upload_and_analyze_section,
 )
 
@@ -88,11 +87,7 @@ for row_start in range(0, len(TOOLS), 3):
 # ---------------------------------------------------------------------------
 
 st.divider()
-footer_left, footer_right = st.columns([4, 1])
-with footer_left:
-    st.caption(
-        "Runs locally. Your data never leaves this computer. "
-        "| DataTools v3.0"
-    )
-with footer_right:
-    quit_button()
+st.caption(
+    "Runs locally. Your data never leaves this computer. "
+    "| DataTools v3.0"
+)