Fix: Add error handling to generate_client_report scan info extraction

ISSUE: Lines 3404-3405 used pipes with grep -v without error handling.
With set -o pipefail enabled, if grep -v returns no matches (exit code 1),
the entire command substitution would fail.

CONTEXT: generate_client_report() function at line 3389, called by main
scan logic to generate client-facing reports after scan completion.

FIXES:
- Line 3404: Added || echo "Unknown" fallback to scan_date extraction
- Line 3405: Added || echo "/" fallback to scan_paths extraction

Ensures variables are always initialized even if patterns don't match.
Maintains consistent error handling with similar code at line 2197.

VERIFIED: bash -n syntax check passes

modules/security/malware-scanner.sh

@@ -3401,8 +3401,8 @@ generate_client_report() {
 
     # Extract scan info
     local session_name=$(basename "$scan_dir")
-    local scan_date=$(grep "Started:" "$summary_file" | head -1 | sed 's/Started: //')
-    local scan_paths=$(sed -n '/^Paths:/,/^$/p' "$summary_file" | tail -n +2 | grep -v "^$" | tr '\n' ', ' | sed 's/, $//')
+    local scan_date=$(grep "Started:" "$summary_file" | head -1 | sed 's/Started: //' || echo "Unknown")
+    local scan_paths=$(sed -n '/^Paths:/,/^$/p' "$summary_file" | tail -n +2 | grep -v "^$" | tr '\n' ', ' | sed 's/, $//' || echo "/")
 
     # Count threats
     local total_threats=0