fix: odstranit firewall roli + pridat btop, mc, tree do base packages

Firewall (UFW) neni pozadovan:
- smazana cela role roles/firewall/
- odstraneny reference z prepare-new-server.yml
- pridana poznamka v group_vars/all.yml.example
- doporuceni: firewall resit externe (Cloudflare Tunnel, security group)

Base packages - pridany chybejici utility:
+ btop (system monitor - lepsi nez htop)
+ mc  (Midnight Commander - textovy file manager)
+ tree (struktura adresaru v terminalu)
Ponechany: curl, wget, git, vim, htop, ca-certificates, gnupg,
          lsb-release, apt-transport-https, bash-completion,
          software-properties-common, unzip, zip, rsync, net-tools

group_vars/all.yml.example

@@ -51,6 +51,10 @@ services_to_deploy:
 # ============================================
 # NETWORK / FIREWALL
 # ============================================
+# POZNAMKA: firewall (UFW) se nenastavuje automaticky.
+# Pokud chces firewall, nastav ho rucne (Cloudflare Tunnel,
+# security group na VPS, docker-network oddeleni, ...).
+# Tato promenna zustava pro pripadnou budouci konfiguraci.
 ssh_port: 22
 allowed_ports:
   - { port: 22, proto: tcp, comment: "SSH" }