Fix critical and high bugs B1-B6

- B1: Replace recursive get_timezone_mount/get_gpu_devices with literal YAML strings
- B3: Expand /home/*/hops glob via compgen -G instead of storing as array literal;
  fix eval echo ~$SUDO_USER -> getent passwd in uninstall
- B4: Correct services source path in setup_firewall (hops_service_definitions.sh -> services)
- B5: Replace all ((x++)) with x=$((x + 1)) to avoid set -e abort on zero pre-increment
- B6: Add Linux-only guard at top of hops entry point

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

uninstall

@@ -126,17 +126,17 @@ EOF
     find_homelab_directory() {
         local POSSIBLE_DIRS=(
             "$HOME/hops"
-            "/home/*/hops"
             "/opt/hops"
             "/srv/hops"
         )
-        
-        # Try to find from running user's home first
+        while IFS= read -r d; do POSSIBLE_DIRS+=("$d"); done < <(compgen -G "/home/*/hops" 2>/dev/null)
+
         if [[ -n "$SUDO_USER" ]]; then
-            local user_home=$(eval echo "~$SUDO_USER")
+            local user_home
+            user_home=$(getent passwd "$SUDO_USER" | cut -d: -f6)
             POSSIBLE_DIRS=("$user_home/hops" "${POSSIBLE_DIRS[@]}")
         fi
-        
+
         HOMELAB_DIR=""
         for dir in "${POSSIBLE_DIRS[@]}"; do
             if [[ -f "$dir/docker-compose.yml" ]]; then