fix: resolve all audit findings in hooks, config, and package list

Security/Functional Fixes:
- firewall-setup.sh: Added WireGuard allow, established/related, DHCP
  (was blocking ALL outbound including VPN - system was non-functional)
- disable-package-management.sh: Preserve /var/lib/dpkg/ for queries
  (was destroying dpkg database with rm -rf)
- encryption-validation.sh: Fixed inverted motd conditional
  (was creating file only if it already existed - backwards)
- kernel-hardening.sh: Removed kernel.exec-shield (Red Hat only)
  Changed user.max_user_namespaces from 0 to 100
- sudo-hardening.sh: Removed Defaults requiretty
  (was breaking GUI-launched sudo via pkexec)
- encryption-setup.sh: Fixed conflicting stdin in luksAddKey
- install-scripts.sh: Fixed embedded firewall (same WireGuard bug)
  Replaced gutted security-hardening stub with real status checker
- GRUB config: Fixed serial_console → serial (invalid terminal name)
- Package list: Removed audispd-plugins (deprecated in Debian 13),
  removed duplicate wireguard/wireguard-tools entries

Reference: Full audit findings from Session 7 JOURNAL.md

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

config/hooks/live/kernel-hardening.sh

@@ -27,9 +27,6 @@ kernel.dmesg_restrict = 1
 # Restrict unprivileged use of BPF
 kernel.unprivileged_bpf_disabled = 1
 
-# Enable ExecShield-like protection
-kernel.exec-shield = 1
-
 # Restrict kernel profiling
 kernel.perf_event_paranoid = 3
 
@@ -40,7 +37,7 @@ kernel.kexec_load = 0
 dev.tty.ldisc_autoload = 0
 
 # Restrict user namespaces
-user.max_user_namespaces = 0
+user.max_user_namespaces = 100
 
 # Disable core dumps for SUID binaries
 fs.suid_dumpable = 0