docs: remove URGENT_SECURITY_STATUS_2026-06-09.md

docs: remove URGENT_SECURITY_STATUS_2026-06-09.md

All items from this TODO document have been completed:
- H1: AIO validation (fd mode, read-only mount)
- H3: SHM_RDONLY attach
- H6: Fixed VAs removed (kva_alloc_pages)
- H7: Tmpfs quotas + overflow hardening
- M2: access() with real IDs
- M6: Overlayfs wrapper lifetime
- M8: CSPRNG (ChaCha20-based DRBG)
- UID Infrastructure: /etc/passwd, auth, login, utmp/wtmp
- L1: ENAMETOOLONG standardization
- L2: getlogin/who/utmp

Document is no longer needed as reference.