Implement reserved username handling for users, LDAP and Keycloak

Add end-to-end support for reserved usernames and tighten CAPTCHA / Keycloak logic.

Changes:

- Makefile: rename EXTRA_USERS → RESERVED_USERNAMES and pass it as --reserved-usernames to the users defaults generator.

- cli/build/defaults/users.py: propagate  flag into generated users, add --reserved-usernames CLI option and mark listed accounts as reserved.

- Add reserved_users filter plugin with  and  helpers for Ansible templates and tasks.

- Add unit tests for reserved_users filters and the new reserved-usernames behaviour in the users defaults generator.

- group_vars/all/00_general.yml: harden RECAPTCHA_ENABLED / HCAPTCHA_ENABLED checks with default('') and explicit > 0 length checks.

- svc-db-openldap: introduce OPENLDAP_PROVISION_* flags, add OPENLDAP_PROVISION_RESERVED and OPERNLDAP_USERS to optionally exclude reserved users from provisioning.

- svc-db-openldap templates/tasks: switch role/group LDIF and user import loops to use OPERNLDAP_USERS instead of the full users dict.

- networks: assign dedicated subnet for web-app-roulette-wheel.

- web-app-keycloak vars: compute KEYCLOAK_RESERVED_USERNAMES_LIST and KEYCLOAK_RESERVED_USERNAMES_REGEX from users | reserved_usernames.

- web-app-keycloak user profile template: inject reserved-username regex into username validation pattern and improve error message, fix SSH public key attribute usage and add component name field.

- web-app-keycloak update/_update.yml: strip subComponents from component payloads before update and disable async/poll for easier debugging.

- web-app-keycloak tasks/main.yml: guard cleanup include with MODE_CLEANUP and keep reCAPTCHA update behind KEYCLOAK_RECAPTCHA_ENABLED.

- user/users defaults: mark system/service accounts (root, daemon, mail, admin, webmaster, etc.) as reserved so they cannot be chosen as login names.

- svc-prx-openresty vars: simplify OPENRESTY_CONTAINER lookup by dropping unused default parameter.

- sys-ctl-rpr-btrfs-balancer: simplify main.yml by removing the extra block wrapper.

- sys-daemon handlers: quote handler name for consistency.

Context: change set discussed and refined in ChatGPT on 2025-11-29 (Infinito.Nexus reserved usernames & Keycloak user profile flow). See conversation: https://chatgpt.com/share/692b21f5-5d98-800f-8e15-1ded49deddc9

group_vars/all/09_networks.yml

@@ -122,6 +122,8 @@ defaults_networks:
       subnet: 192.168.104.112/28
     web-app-littlejs:
       subnet: 192.168.104.128/28
+    web-app-roulette-wheel:
+      subnet: 192.168.104.144/28
 
     # /24 Networks / 254 Usable Clients
     web-app-bigbluebutton: