Fix sidebar toggle, ? shortcut, footer hint styling

- Sidebar: replace 32px overflow:hidden collapse with display:none — eliminates pointer-event/layout issues; button label toggles between 'Filters' and 'Show Filters'
- Keyboard shortcut ?: fix keydown handler to omit shift+ prefix for symbol keys (shift state already encoded in e.key), so '?' registration matches correctly
- Footer: add missing CSS for .lt-footer-hint, .lt-footer-key, .lt-footer-sep — resets button defaults so CFG/HELP render identically to link-style hints

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/js/base.js

@@ -391,7 +391,10 @@
     let combo = '';
     if (e.ctrlKey || e.metaKey) combo += 'ctrl+';
     if (e.altKey)               combo += 'alt+';
-    if (e.shiftKey)             combo += 'shift+';
+    // Only add shift+ for letter keys — for symbol keys (?, !, @, etc.) the shift state
+    // is already encoded in e.key itself, so adding shift+ would break registrations like '?'.
+    const isLetter = e.key.length === 1 && /[a-zA-Z]/.test(e.key);
+    if (e.shiftKey && isLetter) combo += 'shift+';
     combo += e.key.toLowerCase();
     const alwaysFire = e.key === 'Escape' || e.ctrlKey || e.metaKey;
     if (inInput && !alwaysFire) return;