feat(streaming): add emulator streaming backend

Add /api/streaming endpoints for session claim/release, ROM launch,
save states, volume control, and save-and-exit against per-platform
emulator broker containers. Sessions are stored in Redis with atomic
SET NX claims, owner-bound, and admin force-releasable. Config comes
from config.yml (streaming.enabled + containers list) with a
STREAMING_SAVE_TIMEOUT env override for slow-saving brokers.

Includes 19 endpoint tests covering auth scopes, claim races,
ownership, broker failure paths, and force-release.

Author: LoneAngelFayt

backend/config/config_manager.py

@@ -104,6 +104,13 @@ class NetplayICEServer(TypedDict):
     credential: NotRequired[str]
 
 
+class StreamingContainer(TypedDict):
+    platform: str
+    host: str
+    broker_host: str
+    label: str
+
+
 class Config:
     CONFIG_FILE_MOUNTED: bool
     CONFIG_FILE_WRITABLE: bool
@@ -135,6 +142,8 @@ class Config:
     SCAN_MEDIA: list[str]
     GAMELIST_MEDIA_THUMBNAIL: MetadataMediaType
     GAMELIST_MEDIA_IMAGE: MetadataMediaType
+    STREAMING_ENABLED: bool
+    STREAMING_CONTAINERS: list[StreamingContainer]
 
     def __init__(self, **entries):
         self.__dict__.update(entries)
@@ -447,6 +456,10 @@ def _parse_config(self):
             PEGASUS_AUTO_EXPORT_ON_SCAN=pydash.get(
                 self._raw_config, "scan.pegasus.export", False
             ),
+            STREAMING_ENABLED=pydash.get(self._raw_config, "streaming.enabled", False),
+            STREAMING_CONTAINERS=pydash.get(
+                self._raw_config, "streaming.containers", []
+            ),
         )
 
     def _get_ejs_controls(self) -> dict[str, EjsControls]:
@@ -717,6 +730,14 @@ def _validate_config(self):
             )
             self.config.GAMELIST_MEDIA_IMAGE = MetadataMediaType.SCREENSHOT
 
+        if not isinstance(self.config.STREAMING_ENABLED, bool):
+            log.critical("Invalid config.yml: streaming.enabled must be a boolean")
+            sys.exit(3)
+
+        if not isinstance(self.config.STREAMING_CONTAINERS, list):
+            log.critical("Invalid config.yml: streaming.containers must be a list")
+            sys.exit(3)
+
     def get_config(self) -> Config:
         try:
             with open(self.config_file, "r") as config_file: