fix: prevent sudo cache expiry during install and add timezone fallback

Two issues caused the timezone step to fail on first run:

1. Sudo credential cache (default 15 min) can expire during the long
   apt install step before configure_timezone runs. Added `sudo -v`
   immediately after the install confirmation prompt to prime the cache
   as late as possible, just before the first long-running step.

2. `sudo timedatectl set-timezone` can fail with "Access denied" if
   polkit/D-Bus is not yet fully ready in the install environment.
   Added a direct fallback (ln -sf localtime + tee /etc/timezone)
   that bypasses D-Bus entirely.

https://claude.ai/code/session_01M3tiofbGfmTddeMcXr8nXr

ubuntu-based-kiosk-v0.9.9.1.sh

@@ -796,7 +796,14 @@ configure_timezone() {
     
     if [[ -n "$new_tz" ]]; then
         if timedatectl list-timezones | grep -q "^${new_tz}$"; then
-            sudo timedatectl set-timezone "$new_tz" && log_success "Timezone updated to $new_tz"
+            if sudo timedatectl set-timezone "$new_tz"; then
+                log_success "Timezone updated to $new_tz"
+            else
+                # Fallback: set timezone directly without D-Bus
+                sudo ln -sf "/usr/share/zoneinfo/$new_tz" /etc/localtime
+                echo "$new_tz" | sudo tee /etc/timezone > /dev/null
+                log_success "Timezone updated to $new_tz (direct)"
+            fi
         else
             log_error "Invalid timezone: $new_tz"
         fi
@@ -3908,7 +3915,10 @@ first_time_install() {
     echo
     read -r -p "Proceed with installation? (y/n): " proceed
     [[ ! "$proceed" =~ ^[Yy]$ ]] && exit 0
-    
+
+    # Cache sudo credentials upfront so they don't expire mid-install
+    sudo -v
+
     echo
     echo "[1/27] Installing packages..."
     sudo apt update