feat: enhance shortcuts modal and complete logos-to-icons rename

This commit includes graphical keyboard icons integration, modal styling
improvements, and comprehensive "Logos" to "Icons" terminology update.

Changes:
- Add graphical keyboard icons using Iconify MDI (Tab, Ctrl, Cmd, Esc, etc.)
- Implement color scheme: black title, green subtitle/headers, blue kbd elements
- Add visual boxes with borders and shadows for section grouping
- Change modal from 3-column to 2-column grid layout (900px width)
- Fix critical bug: all 5 sections now render (was only showing 2)

Rename "Logos" to "Icons" across entire codebase:
- Go models: ToggleLogos → ToggleIcons, ShowLogos → ShowIcons
- Routes: /toggle/logos → /toggle/icons
- Templates: desktop-logo-toggle → desktop-icon-toggle, #logoToggle → #iconToggle
- JavaScript: logoToggles → iconToggles, sync logic updated
- CSS: .show-logos → .show-icons
- UI JSON: toggleLogos → toggleIcons
- Comments and labels updated

Technical details:
- Rebuilt Go binary to fix template rendering error
- Fixed JSON struct tag: json:"toggleLogos" → json:"toggleIcons"
- Updated kbd element styling for icon alignment (inline-flex)
- Added margin-bottom to subtitle (0.5rem)
- Grid now 2 columns for better 5-section layout

All 5 sections now render correctly:
1. Zoom Control
2. View Controls
3. Navigation
4. Actions
5. Browser Defaults

templates/cv-content.html

@@ -1,5 +1,5 @@
 <main id="cv-content"
-      class="cv-paper {{.CVLengthClass}} {{if .ShowLogos}}show-logos{{end}}"
+      class="cv-paper {{.CVLengthClass}} {{if .ShowIcons}}show-icons{{end}}"
       role="main"
       aria-live="polite">
 <!-- PAGE 1 -->