Add LiveKit, coturn, and JWT service to Matrix module

- Integrate LiveKit SFU, coturn TURN server, and lk-jwt-service for
  Element Call support in the Matrix Synapse module
- Add firewall rules for new services and ports
- Add key generation systemd service for LiveKit JWT
- Extend Synapse config with TURN URIs and experimental features
- Update Caddy config for new endpoints and well-known support
- Improve OIDC config with additional scopes and user mapping
- Add Grafana secret_key to SOPS secrets and config
- Refactor and modularize secret checking in justfile scripts

.just/machine.just

@@ -7,5 +7,6 @@
 [doc('Update the target machine')]
 [no-exit-message]
 @update machine:
+    cd .. && just vars _check {{ machine }}
     just assert '-d "../systems/x86_64-linux/{{ machine }}"' "Machine {{ machine }} does not exist, must be one of: $(ls ../systems/x86_64-linux/ | sed ':a;N;$!ba;s/\n/, /g')"
     nixos-rebuild switch -L --sudo --target-host {{ machine }} --build-host {{ machine }} --flake ..#{{ machine }} --log-format internal-json -v |& nom --json