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

Makefile

@@ -11,7 +11,7 @@ INCLUDE_GROUPS := $(shell python3 main.py meta categories invokable -s "-" --no-
 INCLUDES_OUT_DIR    := ./tasks/groups
 
 # Compute extra users as before
-EXTRA_USERS := $(shell \
+RESERVED_USERNAMES := $(shell \
   find $(ROLES_DIR) -maxdepth 1 -type d -printf '%f\n' \
     | sed -E 's/.*-//' \
     | grep -E -x '[a-z0-9]+' \
@@ -50,7 +50,7 @@ messy-build: dockerignore
 	python3 $(USERS_SCRIPT) \
 	  --roles-dir $(ROLES_DIR) \
 	  --output $(USERS_OUT) \
-	  --extra-users "$(EXTRA_USERS)"
+	  --reserved-usernames "$(RESERVED_USERNAMES)"
 	@echo "✅ Users defaults written to $(USERS_OUT)\n"
 
 	@echo "🔧 Generating applications defaults → $(APPLICATIONS_OUT)…"