Malware scanner: Fix input validation bugs (CRITICAL)

Fixed critical bugs where non-numeric user input could cause bash errors
when used in integer comparisons.

**Bug: Unvalidated numeric input in 3 locations**

Problem: User input used directly in integer comparisons without validation
Impact: Bash error "integer expression expected" if user enters text
Locations:
- Line 1647: delete_standalone_sessions() - delete choice
- Line 1776: view_scan_results() - scanner choice
- Line 1848: view_scan_results() - session choice

Example failure:
  User enters: "abc"
  Code: if [ "$choice" -lt 1 ]
  Error: "bash: [: abc: integer expression expected"

**Fix: Add regex validation before integer comparisons**

Added numeric validation using regex before all integer comparisons:
  if ! [[ "$input" =~ ^[0-9]+$ ]]; then
      echo "Invalid choice (must be a number)"
      return 1
  fi

Changes to delete_standalone_sessions():
- Added numeric check at line 1648 before integer comparison
- Improved error message: "must be a number" vs "out of range"

Changes to view_scan_results() (2 locations):
- Added numeric check at line 1777 (scanner choice)
- Added numeric check at line 1845 (session choice)
- Both get validation before integer comparisons

Why this is critical:
- Prevents bash errors from crashing the script
- Provides clear error messages to users
- Handles edge case of accidental text input
- Common user error (typing letters instead of numbers)

Testing: Syntax validated, input validation working

modules/security/malware-scanner.sh

@@ -1644,8 +1644,15 @@ delete_standalone_sessions() {
             ;;
         *)
             # Delete specific session
+            # Validate numeric input
+            if ! [[ "$delete_choice" =~ ^[0-9]+$ ]]; then
+                echo -e "${RED}Invalid choice (must be a number)${NC}"
+                read -p "Press Enter to continue..."
+                return 1
+            fi
+
             if [ "$delete_choice" -lt 1 ] || [ "$delete_choice" -gt ${#standalone_dirs[@]} ]; then
-                echo -e "${RED}Invalid choice${NC}"
+                echo -e "${RED}Invalid choice (out of range)${NC}"
                 read -p "Press Enter to continue..."
                 return 1
             fi
@@ -1766,8 +1773,15 @@ view_scan_results() {
 
             read -p "Scanner: " scanner_choice
 
+            # Validate numeric input
+            if ! [[ "$scanner_choice" =~ ^[0-9]+$ ]]; then
+                echo -e "${RED}Invalid choice (must be a number)${NC}"
+                read -p "Press Enter to continue..."
+                return 1
+            fi
+
             if [ "$scanner_choice" -lt 1 ] || [ "$scanner_choice" -gt ${#available_scanners[@]} ]; then
-                echo -e "${RED}Invalid choice${NC}"
+                echo -e "${RED}Invalid choice (out of range)${NC}"
                 read -p "Press Enter to continue..."
                 return 1
             fi
@@ -1827,12 +1841,19 @@ view_scan_results() {
 
             read -p "Select session (or 0 to cancel): " session_choice
 
+            # Validate numeric input
+            if ! [[ "$session_choice" =~ ^[0-9]+$ ]]; then
+                echo -e "${RED}Invalid choice (must be a number)${NC}"
+                read -p "Press Enter to continue..."
+                return 1
+            fi
+
             if [ "$session_choice" = "0" ]; then
                 return 0
             fi
 
             if [ "$session_choice" -lt 1 ] || [ "$session_choice" -gt ${#standalone_dirs[@]} ]; then
-                echo -e "${RED}Invalid choice${NC}"
+                echo -e "${RED}Invalid choice (out of range)${NC}"
                 read -p "Press Enter to continue..."
                 return 1
             fi