3.0.4: fix: Guard admin-only function call and strengthen UTF-8 sanitization

• FIX: Resolve SQL error "Could not perform query because it contains invalid data" caused by invalid UTF-8 byte sequences in URLs. Added sanitization to strip invalid UTF-8 characters before database storage.
• FIX: Resolve "Table doesn't exist" errors on case-sensitive MySQL installations (lower_case_table_names=0) with mixed-case WordPress prefixes. All plugin table references now use normalized lowercase prefixes to match table creation behavior.