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-base/README.md

@@ -0,0 +1,21 @@
+# Front Base (HTTPS + Cloudflare + Handlers) 🚀
+
+## Description
+**sys-stk-front-base** bootstraps the front layer that most web-facing apps need:
+- Ensures the HTTPS base via `sys-svc-webserver-https`
+- (Optional) Cloudflare bootstrap (zone lookup, dev mode, purge)
+- Wires OpenResty/Nginx handlers
+- Leaves per-domain certificate issuance to consumer roles (or pass-through vars to `sys-util-csp-cert` if needed)
+
+> This role is intentionally small and reusable. It prepares the ground so app roles can just render their vHost.
+
+## Responsibilities
+- Include `sys-svc-webserver-https` (once per host)
+- Include Cloudflare tasks when `DNS_PROVIDER == "cloudflare"`
+- Load handler utilities (e.g., `svc-prx-openresty`)
+- Stay domain-agnostic: expect `domain` to be provided by the consumer
+
+## Outputs
+- Handler wiring completed
+- HTTPS base ready (Nginx, ACME webroot)
+- Cloudflare prepared (optional)