Add Help menu and contextual tooltips to GUI

- Add Help menu with quick guides: Getting Started, Create Tool,
  Install Tools, Publish Tools, Keyboard Shortcuts, About
- F1 shortcut opens Getting Started guide
- Add tooltips to Tool Builder section headings (Arguments, Steps,
  Output Template) that appear on hover over the label text
- Add tooltips to Registry page controls (search, filters, pagination)
- Enhance sidebar tooltips with keyboard shortcuts

Co-Authored-By: Claude Opus 4.5 <[email protected]>

src/cmdforge/gui/styles.py

@@ -225,6 +225,12 @@ QLabel#label {
     color: #4a5568;
 }
 
+QLabel#sectionHeading {
+    font-weight: 600;
+    font-size: 13px;
+    color: #2d3748;
+}
+
 /* Scrollbars */
 QScrollBar:vertical {
     background-color: #f7fafc;