Merge remote-tracking branch 'origin/master' into dev

Brings the go2rtc security fixes from #24658 to dev. Dev-specific changes
in the merge:
- frigate/config/env.py stays deleted; the environment_vars protection for
  GO2RTC_ALLOW_ARBITRARY_EXEC moves to apply_config_env_vars in
  frigate/util/env.py, so the value never reaches os.environ
- services.py imports substitute_frigate_vars from frigate.util.env and
  maps UnknownVariableError to the unknown variable message
- go2rtc stream tests patch dev's import-time exec override snapshot and
  its FRIGATE_* variable sources
- test_http_media.py keeps dev's _insert_recording helper; the one added
  on master replaced it and broke the dev tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/public/locales/en/views/settings.json

@@ -1116,6 +1116,7 @@
         "title": "Create New User",
         "desc": "Add a new user account and specify a role for access to areas of the Frigate UI.",
         "usernameOnlyInclude": "Username may only include letters, numbers, . or _",
+        "usernameOnlyDots": "Username cannot contain only periods",
         "confirmPassword": "Please confirm your password"
       },
       "deleteUser": {