dual-gpu & audio fixes + flatpak migration

- Fixed `set -euo pipefail` crashes across hardware detection: Added `|| true` guards to all `nvidia-smi`, `dpkg -l`, `apt-cache policy`, and `nvidia-detect` pipelines in `sysinfo.sh` (3 lines) and `gpu/nvidia.sh` (7+ lines).
- Created new Audio & Sound module (`modules/extras/audio/audio.sh`) with Debian version-specific logic: Bullseye basic mode vs Bookworm/Trixie standard PipeWire stack, plus ALSA utilities, pavucontrol, pulsemixer, playerctl. Added menu entry "14 Audio & Sound".
- Migrated Flatpak from System Tools to Software Center category. Renamed menu to "Software Center & Flatpak", converted single-select to multi-select checklist in `software_centers.sh`, removed logic from `system.sh`.
- Implemented robust time synchronization: New `_ensure_time_synced()` function in `utils.sh` forces NTP active, validates timezone with interactive `dpkg-reconfigure tzdata` if needed, restarts `systemd-timesyncd`, and verifies sync status. Replaced `check_system_time` call in main script.
- Fixed System Info network detection: Removed hardcoded 2-line height limit (now dynamic via terminal size), fixed hard-coded array indices to use progressive counters for multiple interfaces including USB WiFi adapters.

modules/extras.sh

@@ -39,11 +39,12 @@ install_extras() {
             "7" "Code Editors & IDEs" \
             "8" "Servers & Dev Tools" \
             "9" "Security & Networking" \
-            "10" "Software Centers" \
+            "10" "Software Center & Flatpak" \
             "11" "Office & Productivity" \
             "12" "System Tools" \
             "13" "Fetch / System Info" \
-            "14" "Back to main menu")
+            "14" "Audio & Sound" \
+            "15" "Back to main menu")
 
         [ -z "$cat_choice" ] && return
         clear
@@ -63,7 +64,8 @@ install_extras() {
             11) _cat_office ;;
             12) _cat_general ;;
             13) _cat_fetch ;;
-            14) return ;;
+            14) _cat_audio ;;
+            15) return ;;
         esac
         clear
     done