fix: Mobile hamburger menu and iPad sidebar visibility

Mobile fixes:
- Add click toggle handler for hamburger menu (was hover-only)
- Menu now opens/closes on tap and closes when clicking outside
- Keep hover support for desktop

iPad fixes:
- Sidebar content now visible on touch devices (901-1280px)
- Added (hover: hover) media query to prevent hide-on-hover on tablets

Security improvements:
- Replace exec.CommandContext with go-git library for git operations
- Add path traversal and command injection prevention
- Fix race condition in template hot reload
- Add environment-based cookie Secure flag

Code quality:
- Add constants.go for magic numbers
- Remove unused code (ParsePreferenceToggleRequest, DomainError)
- Add FOUC prevention with inline critical CSS
- Add Makefile dev/run/clean targets
- Fix README git clone URL
- Add doc/DECISIONS.md for architectural decisions

Tests:
- Add hamburger menu click toggle tests
- Add iPad sidebar visibility tests
- Update security tests for go-git implementation
- Add cookie Secure flag tests

static/js/main.js

@@ -24,7 +24,8 @@
 
     /**
      * Initialize minimal menu control system
-     * CSS handles most logic, JS just bridges hamburger to menu
+     * CSS handles most logic, JS bridges hamburger to menu
+     * Click toggle for mobile, hover for desktop
      */
     function initMenuSystem() {
         const hamburgerBtn = document.querySelector('.hamburger-btn');
@@ -32,7 +33,20 @@
 
         if (!hamburgerBtn || !menu) return;
 
-        // Show menu on hamburger hover - CSS handles the rest
+        // Click handler for mobile - toggles menu-open class
+        hamburgerBtn.addEventListener('click', (e) => {
+            e.stopPropagation();
+            menu.classList.toggle('menu-open');
+        });
+
+        // Close menu when clicking outside (for mobile)
+        document.addEventListener('click', (e) => {
+            if (!menu.contains(e.target) && !hamburgerBtn.contains(e.target)) {
+                menu.classList.remove('menu-open');
+            }
+        });
+
+        // Desktop hover support - show menu on hamburger hover
         hamburgerBtn.addEventListener('mouseenter', () => menu.classList.add('menu-hover'));
 
         // Hide menu when leaving hamburger if not hovering menu