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

Makefile

@@ -1,4 +1,4 @@
-.PHONY: test test-all test-unit test-integration lint build
+.PHONY: test test-all test-unit test-integration lint build dev run clean
 
 # Default: Run unit tests only (fast, no Chrome needed)
 test: test-unit
@@ -28,6 +28,21 @@ build:
 	@echo "🔨 Building..."
 	go build -v -o cv-server .
 
+# Run in development mode with hot reload
+dev:
+	@echo "🚀 Starting development server with hot reload..."
+	GO_ENV=development TEMPLATE_HOT_RELOAD=true go run main.go
+
+# Run in production mode
+run:
+	@echo "🚀 Starting server..."
+	go run main.go
+
+# Clean build artifacts
+clean:
+	@echo "🧹 Cleaning build artifacts..."
+	rm -f cv-server coverage.txt coverage-report.txt benchmark.txt
+
 # Run all checks (lint + unit tests)
 check: lint test-unit
 	@echo "✅ All checks passed!"