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

templates/index.html

@@ -39,7 +39,36 @@
     <!-- HTMX Configuration -->
     <meta name="htmx-config" content='{"timeout":5000,"defaultSwapStyle":"innerHTML","defaultSwapDelay":0,"defaultSettleDelay":20}'>
 
-    <!-- FOUC Prevention: Apply color theme before page render -->
+    <!-- FOUC Prevention: Inline critical CSS + Apply color theme before page render -->
+    <!-- Critical theme variables inlined to prevent flash of unstyled content -->
+    <style>
+      /* Light theme (default) - critical variables only */
+      :root {
+        --page-bg: #d6d6d6;
+        --paper-bg: #ffffff;
+        --text-primary: #1a1a1a;
+        --sidebar-bg: #d1d4d2;
+      }
+      /* Dark theme - critical variables only */
+      [data-color-theme="dark"] {
+        --page-bg: #3a3a3a;
+        --paper-bg: #1a1a1a;
+        --text-primary: #e0e0e0;
+        --sidebar-bg: #3a3d3e;
+      }
+      /* Auto theme follows system preference */
+      @media (prefers-color-scheme: dark) {
+        [data-color-theme="auto"] {
+          --page-bg: #3a3a3a;
+          --paper-bg: #1a1a1a;
+          --text-primary: #e0e0e0;
+          --sidebar-bg: #3a3d3e;
+        }
+      }
+      /* Apply critical styles immediately */
+      html { background-color: var(--page-bg); }
+      body { color: var(--text-primary); }
+    </style>
     <script>
     (function() {
       let theme = localStorage.getItem('color-theme-mode');