fix(footer,nav): left-justify buttons, drop per-page caption bar, hide sidebar Close

Three small follow-ups to the sticky-footer rework:

- Left-justify the footer buttons (and reposition the Help popover
  to anchor at the left edge so it lines up with its trigger).
- Remove the per-page ``st.divider() + st.caption("Runs locally…")``
  trailing block from all 9 tool pages. The new sticky footer
  covers that text, so it was rendering as an empty white bar at
  the bottom of each tool page.
- Hide the Close entry from the sidebar nav via CSS. The page stays
  registered with st.navigation so /close is still routable for the
  sticky-footer Close button — only the sidebar link + its section
  header are hidden (via :has() on stNavSection).

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

src/gui/pages/9_Pipeline_Runner.py

@@ -419,9 +419,6 @@ with dl_c:
     )
 
 
-st.divider()
-st.caption("Runs locally. Your data never leaves this computer. | DataTools v3.0")
-
 # ---------------------------------------------------------------------------
 # Post-run auto-scroll
 # ---------------------------------------------------------------------------