Add comprehensive user permission validation and clear error messages

Improvements:

1. Enhanced root permission check (Lines 24-37)
   - Clear error message explaining why root is required
   - Lists all permission-required operations:
     - Read access to /var/lib/mysql
     - Create directories in /home
     - Change file ownership
     - Start mysqld daemon
     - Access system config files
   - Provides sudo command suggestion

2. MySQL data directory read permission check (Lines 189-231)
   - Validates read access to detected MySQL directory
   - Checks after each detection method (running MySQL, config, default)
   - Provides helpful error message if permission denied
   - Suggests running with sudo

3. Clear error messaging throughout
   - Users now understand WHY permission is denied
   - Actionable guidance (use sudo)
   - Consistent error format

Impact:
- Prevents confusing silent failures deep in workflow
- Users immediately know if they need to use sudo
- Better debugging experience
- Professional error handling

Before: User runs script, goes through 3 steps, then fails with:
        "Permission denied" with no context

After: User immediately sees:
       "PERMISSION DENIED: This script must be run as root"
       Lists exact reasons why
       Suggests: "sudo ./script.sh"

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

modules/backup/mysql-restore-to-sql.sh

@@ -23,7 +23,19 @@ source "$SCRIPT_DIR/lib/system-detect.sh"
 
 # Root check
 if [ "$EUID" -ne 0 ]; then
-    print_error "This script must be run as root"
+    echo ""
+    print_error "PERMISSION DENIED: This script must be run as root"
+    echo ""
+    echo "Why root is required:"
+    echo "  - Read access to live MySQL data directory (/var/lib/mysql)"
+    echo "  - Create directories in /home (for temporary restore location)"
+    echo "  - Change file ownership to mysql:mysql"
+    echo "  - Start MySQL daemon (mysqld) process"
+    echo "  - Access system configuration files"
+    echo ""
+    echo "To run this script:"
+    echo "  sudo $0 $*"
+    echo ""
     exit 1
 fi
 
@@ -182,6 +194,12 @@ detect_mysql_datadir() {
         LIVE_DATADIR=$(mysql -NBe 'SELECT @@datadir;' 2>/dev/null)
         if [ -n "$LIVE_DATADIR" ]; then
             echo "  Detected from running MySQL: $LIVE_DATADIR"
+            # Verify we can read this directory
+            if [ ! -r "$LIVE_DATADIR" ]; then
+                print_error "Cannot read MySQL data directory: Permission denied"
+                print_info "Try running this script with: sudo $0"
+                return 1
+            fi
             return 0
         fi
     fi
@@ -191,6 +209,12 @@ detect_mysql_datadir() {
     if [ -n "$config_dir" ]; then
         LIVE_DATADIR="$config_dir"
         echo "  Detected from config: $LIVE_DATADIR"
+        # Verify we can read this directory
+        if [ ! -r "$LIVE_DATADIR" ]; then
+            print_error "Cannot read MySQL data directory: Permission denied"
+            print_info "Try running this script with: sudo $0"
+            return 1
+        fi
         return 0
     fi
 
@@ -198,6 +222,12 @@ detect_mysql_datadir() {
     if [ -d "/var/lib/mysql" ]; then
         LIVE_DATADIR="/var/lib/mysql"
         echo "  Using default: $LIVE_DATADIR"
+        # Verify we can read this directory
+        if [ ! -r "$LIVE_DATADIR" ]; then
+            print_error "Cannot read MySQL data directory: Permission denied"
+            print_info "Try running this script with: sudo $0"
+            return 1
+        fi
         return 0
     fi