feat(multi-user): add unclaimed doc visibility, claim/assign-owner endpoints, default_owner_id

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/config.py

@@ -134,6 +134,24 @@ class Settings(BaseSettings):
             "Individual user limits can override this default. Default: 0 (unlimited)."
         ),
     )
+    unowned_docs_visible_to_all: bool = Field(
+        default=True,
+        description=(
+            "In multi-user mode, controls whether documents without an owner (owner_id is NULL) "
+            "are visible to all authenticated users. When True, unowned documents appear in every "
+            "user's file list alongside their own files. When False, only admins can see unowned "
+            "documents. Default: True."
+        ),
+    )
+    default_owner_id: Optional[str] = Field(
+        default=None,
+        description=(
+            "When set, automatically assigns this owner ID to newly ingested documents that would "
+            "otherwise have no owner (e.g. documents from IMAP, API without session, or legacy imports). "
+            "Use the admin /api/files/assign-owner endpoint to bulk-assign existing unclaimed documents. "
+            "Default: None (documents remain unowned until claimed)."
+        ),
+    )
 
     # Authentik
     authentik_client_id: Optional[str] = None