✨(backend) add configuration for idle disconnect timeout

Expose idle disconnect timeout as configurable parameter accepting None value
to disable feature entirely, providing emergency killswitch for buggy behavior
without redeployment, following other frontend configuration patterns.

src/backend/meet/settings.py

@@ -326,6 +326,11 @@ class Base(Configuration):
         "is_silent_login_enabled": values.BooleanValue(
             True, environ_name="FRONTEND_IS_SILENT_LOGIN_ENABLED", environ_prefix=None
         ),
+        "idle_disconnect_warning_delay": values.PositiveIntegerValue(
+            None,
+            environ_name="FRONTEND_IDLE_DISCONNECT_WARNING_DELAY",
+            environ_prefix=None,
+        ),
         "feedback": values.DictValue(
             {}, environ_name="FRONTEND_FEEDBACK", environ_prefix=None
         ),

src/frontend/src/api/useConfig.ts

@@ -25,6 +25,7 @@ export interface ApiConfig {
   custom_css_url?: string
   use_french_gov_footer?: boolean
   use_proconnect_button?: boolean
+  idle_disconnect_warning_delay?: number
   recording?: {
     is_enabled?: boolean
     available_modes?: RecordingMode[]