fix: NetBird je samostatna aplikace (apt balicek), ne Docker sluzba

roles/netbird/tasks/main.yml:
- apt balicek 'netbird' (oficialni NetBird Linux klient)
- neni Docker, neni sluzba - je to VPN klient

roles/netbird/defaults/main.yml:
- odebrano netbird_run_as_system_service (nepotreba)
- pridana poznamka o instalaci

playbook priprav-novy-server.yml:
- hlavicka: 'NetBird (mesh VPN klient - apt balicek, NE Docker)'

group_vars/all.yml.example:
- pridana dokumentace https://docs.netbird.io/get-started/install
- komentare rikaji, ze to neni Docker sluzba

README.md:
- tabulka roli: 'apt balicek, ne Docker'
- krok 8: 'NetBird (mesh VPN klient - apt balicek)'

Postup instalace:
- Linux server: ansible role -> apt install netbird
- macOS workstation: brew install --cask netbird (v Brewfile)
- Windows: instalator z netbird.io
- Registrace: netbird up --setup-key <key> (z app.netbird.io)

roles/netbird/defaults/main.yml

@@ -1,15 +1,21 @@
 ---
 # Promenne pro netbird roli
-# NetBird - WireGuard-based mesh VPN (https://netbird.io)
-
-# Setup klice pro NetBird registraci
+# NetBird - WireGuard-based mesh VPN klient (https://netbird.io)
+#
+# POZNAMKA: NetBird je samostatna aplikace (klient), NE Docker sluzba.
+# - Linux: instaluje se jako apt balicek (netbird)
+# - macOS: instaluje se pres brew cask (netbird)
+# - Windows: instalator z netbird.io
+# Viz: https://docs.netbird.io/get-started/install
+#
+# Setup key pro automatickou registraci (po prvnim spusteni).
 # Najdes v NetBird dashboardu: https://app.netbird.io/ -> Setup Keys
 # Napr: AAAA-BBBB-CCCC-DDDD-EEEE
+#
+# Pokud je prazdne, NetBird se pouze nainstaluje - registraci provedes rucne:
+#   netbird up --setup-key <tvuj-key>
+#
 netbird_setup_key: ""
 
-# NetBird spust jako systemova sluzba (root)
-# Pro user-level: netbird up --setup-key XXX (interaktivni)
-netbird_run_as_system_service: true
-
 # Vychozi Management Server (self-hosted nebo oficialni)
 netbird_management_url: "https://api.netbird.io"