BizCore v2.6 Responsive Sidebar & Stability Cleanup

INSTALL
1. Take a full BizCore files backup.
2. Export the database as an additional safety backup.
3. Upload this ZIP to:
   /public_html/ceylongemx.online/
4. Extract and overwrite.
5. Login as Super Admin.
6. Open:
   https://ceylongemx.online/update-2.6.php
7. Click Install v2.6 Update.
8. Press Ctrl + F5.

WHAT CHANGED
- Left menu now scrolls independently from the page.
- ☰ button hides/shows the menu on desktop.
- Mobile menu opens as a slide-out panel.
- Desktop collapsed preference is saved in localStorage.
- Finance dashboard account queries now use qualified table aliases.
- Company and workspace pages use safe fallback values.
- Existing database records and inventory transactions are preserved.

IMPORTANT
The earlier log showed:
- Undefined array key warnings on company/workspace pages.
- An ambiguous status column in finance-dashboard.php.
- Historical Too many connections errors.

This release fixes the first two code issues. The Database class already uses one
static PDO connection per PHP request, so a hosting-level connection limit should
be checked separately only if Too many connections appears again after this update.
