✨(backend) add roomkit viewset to start a room without WebRTC join

Introduce a new viewset that lets the roomkit start a room even when
no WebRTC participant has joined yet.

This is a first entry point that will be extended over time with
more actions a roomkit needs to be able to trigger.

Known limitations:

* The responsibility around SIP rules is currently split between
  the telephony feature and the roomkit one. This may need a
  refactor later on to consolidate ownership in a single place.
* The default throttle might be too low for production usage and
  will likely need to be revisited.

src/backend/core/services/livekit_events.py

@@ -245,7 +245,7 @@ class LiveKitEventsService:
         except models.Room.DoesNotExist as err:
             raise ActionFailedError(f"Room with ID {room_id} does not exist") from err
 
-        if settings.ROOM_TELEPHONY_ENABLED:
+        if settings.ROOM_TELEPHONY_ENABLED or settings.ROOMKIT_ENABLED:
             try:
                 self.telephony_service.create_dispatch_rule(room)
             except TelephonyException as e:
@@ -265,7 +265,7 @@ class LiveKitEventsService:
             )
             raise ActionFailedError("Failed to process room finished event") from e
 
-        if settings.ROOM_TELEPHONY_ENABLED:
+        if settings.ROOM_TELEPHONY_ENABLED or settings.ROOMKIT_ENABLED:
             try:
                 self.telephony_service.delete_dispatch_rule(room_id)
             except TelephonyException as e:

src/backend/core/services/telephony.py

@@ -3,7 +3,7 @@
 from logging import getLogger
 
 from asgiref.sync import async_to_sync
-from livekit.api import TwirpError
+from livekit.api import TwirpError, TwirpErrorCode
 from livekit.protocol.sip import (
     CreateSIPDispatchRuleRequest,
     DeleteSIPDispatchRuleRequest,
@@ -21,6 +21,10 @@ class TelephonyException(Exception):
     """Exception raised when telephony operations fail."""
 
 
+class DispatchRuleConflictError(TelephonyException):
+    """Raised when a dispatch rule already exists for the same routing criteria."""
+
+
 class TelephonyService:
     """Service for managing participant access through the telephony system (SIP)."""
 
@@ -51,6 +55,8 @@ class TelephonyService:
         try:
             await lkapi.sip.create_sip_dispatch_rule(create=request)
         except TwirpError as e:
+            if e.code == TwirpErrorCode.ALREADY_EXISTS:
+                raise DispatchRuleConflictError("Dispatch rule already exists") from e
             logger.exception(
                 "Unexpected error creating dispatch rule for room %s", room.id
             )
@@ -94,6 +100,28 @@ class TelephonyService:
             if existing_rule.name == rule_name
         ]
 
+    @async_to_sync
+    async def has_dispatch_rule(self, room_id):
+        """Check whether at least one dispatch rule exists for a specific room."""
+        return bool(await self._list_dispatch_rules_ids(room_id))
+
+    def ensure_dispatch_rule(self, room):
+        """Create the SIP dispatch rule for a room if it does not already exist.
+
+        Returns:
+            bool: True if a rule was created, False if it already existed.
+        """
+
+        if self.has_dispatch_rule(room.pk):
+            return False
+
+        try:
+            self.create_dispatch_rule(room)
+        except DispatchRuleConflictError:
+            return False
+
+        return True
+
     @async_to_sync
     async def delete_dispatch_rule(self, room_id):
         """Delete all SIP inbound dispatch rules associated with a specific room."""