Rename CVE/vulnerability language to advisory/threat/fix across the stack:
- Dashboard: installed_cve_count→open_threat_count, security_update_count→available_fix_count
- Update detail: Known Vulnerabilities→Security Advisories
- AdvisoryType() helper for human-readable advisory ID prefixes
- clearVulnsOnInstall on installed transition with per-advisory security event logging
- StatsHandler takes checkInInterval for online/offline threshold
- AttentionPanel re-keyed on open-threats / available-fixes
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