refactor(front-stack): introduce sys-stk-front-base and semi-stateless stack; improve coturn role docs

- Extract common HTTPS + Cloudflare + handler bootstrap into new role sys-stk-front-base
- Update sys-stk-front-proxy, web-svc-cdn, web-svc-file, web-svc-html to depend on sys-stk-front-base
- Add new sys-stk-semi-stateless role combining front-base + back-stateless
- Update web-svc-coturn to use sys-stk-semi-stateless and rewrite README/meta with detailed Coturn description
- Unify sys-util-csp-cert README heading

Ref: ChatGPT conversation https://chatgpt.com/share/68d6cea2-3570-800f-acb3-c3277317f17b

roles/sys-stk-front-proxy/tasks/01_base.yml

@@ -1,17 +1,6 @@
-- block:
-  - name: Include dependency 'sys-svc-webserver-https'
-    include_role:
-      name: sys-svc-webserver-https
-    when: run_once_sys_svc_webserver_https is not defined
-  - include_tasks: utils/run_once.yml
-  when: run_once_sys_stk_front_proxy is not defined
-
-- include_tasks: "02_cloudflare.yml"
-  when: DNS_PROVIDER == "cloudflare"
-
-- include_tasks: "{{ [ playbook_dir, 'tasks/utils/load_handlers.yml' ] | path_join }}"
-  vars:
-    handler_role_name: "svc-prx-openresty"
+- name: Front bootstrap
+  include_role:
+    name: sys-stk-front-base
 
 - name: "include role for '{{ domain }}' to receive certificates and do the modification routines"
   include_role: