Document that Matrix RTC requires the federation port even with federation disabled

LiveKit JWT Service verifies OpenID tokens via the homeserver's
federation API, which it discovers over the public network.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/5540

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/configuring-playbook-matrix-rtc.md

@@ -36,7 +36,7 @@ matrix_rtc_enabled: true
 
 ## Adjusting firewall rules
 
-In addition to the HTTP/HTTPS ports (which you've already exposed as per the [prerequisites](prerequisites.md) document), you'll also need to open ports required by [LiveKit Server](configuring-playbook-livekit-server.md) as described in its own [Adjusting firewall rules](configuring-playbook-livekit-server.md#adjusting-firewall-rules) section.
+In addition to the HTTP/HTTPS ports and the Matrix Federation port (`8448`, required **even with federation disabled**), which you've already exposed as per the [prerequisites](prerequisites.md) document, you'll also need to open ports required by [LiveKit Server](configuring-playbook-livekit-server.md) as described in its own [Adjusting firewall rules](configuring-playbook-livekit-server.md#adjusting-firewall-rules) section.
 
 ## Fronting the integrated reverse-proxy with another reverse-proxy
 

docs/prerequisites.md

@@ -57,7 +57,7 @@ We will be using `example.com` as the domain in the following instruction. Pleas
 
   - `80/tcp`: HTTP webserver
   - `443/tcp` and `443/udp`: HTTPS webserver
-  - `8448/tcp` and `8448/udp`: Matrix Federation API HTTPS webserver. Some components like [Matrix User Verification Service](configuring-playbook-user-verification-service.md#open-matrix-federation-port) require this port to be opened **even with federation disabled**.
+  - `8448/tcp` and `8448/udp`: Matrix Federation API HTTPS webserver. Some components like [Matrix User Verification Service](configuring-playbook-user-verification-service.md#open-matrix-federation-port) and the [Matrix RTC stack](configuring-playbook-matrix-rtc.md) require this port to be opened **even with federation disabled**.
   - potentially some other ports, depending on the additional (non-default) services that you enable in the **configuring the playbook** step (later on). Consult each service's documentation page in `docs/` for that.
 
 ---------------------------------------------