feat(file-storage): add settings, key builder, and backend factory

surfsense_backend/app/file_storage/settings.py

@@ -0,0 +1,37 @@
+"""Environment-driven configuration for the file-storage module."""
+
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+LOCAL_BACKEND = "local"
+AZURE_BACKEND = "azure"
+
+# surfsense_backend/ — two levels up from app/file_storage/settings.py
+_BACKEND_ROOT = Path(__file__).resolve().parents[2]
+_DEFAULT_LOCAL_ROOT = str(_BACKEND_ROOT / ".local_object_store")
+
+
+@dataclass(frozen=True)
+class StorageSettings:
+    """Resolved storage configuration for the current process."""
+
+    backend: str
+    azure_connection_string: str | None
+    azure_container: str | None
+    local_root: str
+
+
+def load_storage_settings() -> StorageSettings:
+    """Read storage settings from the environment.
+
+    Defaults to the ``local`` backend so development needs no cloud creds.
+    """
+    return StorageSettings(
+        backend=os.getenv("FILE_STORAGE_BACKEND", LOCAL_BACKEND).strip().lower(),
+        azure_connection_string=os.getenv("AZURE_STORAGE_CONNECTION_STRING"),
+        azure_container=os.getenv("AZURE_STORAGE_CONTAINER"),
+        local_root=os.getenv("FILE_STORAGE_LOCAL_PATH", _DEFAULT_LOCAL_ROOT),
+    )