fix(onedrive): normalize folder_path for Graph delta URL (#15503)

Prepend a leading slash and reject `..` segments so scoped OneDrive
delta queries use `root:/path:/delta` instead of `root:path:/delta`.

Fixes #15500

### What problem does this PR solve?

The OneDrive connector builds Microsoft Graph delta URLs from optional
`config.folder_path`. When users enter a path without a leading slash
(e.g. `Documents/Reports` instead of `/Documents/Reports`), the
connector produces a malformed URL such as
`root:Documents/Reports:/delta`. Per [Microsoft Graph path-based
addressing](https://learn.microsoft.com/en-us/graph/onedrive-addressing-driveitems),
the segment after `root:` must start with `/` (e.g.
`root:/Documents/Reports:/delta`). Sync and validation then fail or
return no documents, which is hard to diagnose from the UI because the
optional folder field does not enforce the format.

This PR normalizes `folder_path` at connector construction time (prepend
`/`, trim whitespace and trailing slashes) and rejects `..` segments
before any Graph request is made.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

common/data_source/onedrive_connector.py

@@ -32,6 +32,21 @@ _SUPPORTED_EXTENSIONS = {
 }
 
 
+def _normalize_folder_path(folder_path: str | None) -> str | None:
+    """Normalize Graph path-based addressing segment (root:{path}:/delta)."""
+    if folder_path is None:
+        return None
+    path = folder_path.strip()
+    if not path:
+        return None
+    segments = [segment for segment in path.split("/") if segment]
+    if ".." in segments:
+        raise ConnectorValidationError("folder_path must not contain '..' segments.")
+    if not segments:
+        return None
+    return "/" + "/".join(segments)
+
+
 class OneDriveCheckpoint(ConnectorCheckpoint):
     """OneDrive-specific checkpoint tracking delta links per drive."""
     delta_links: dict[str, str] | None = None
@@ -52,7 +67,7 @@ class OneDriveConnector(CheckpointedConnectorWithPermSync, SlimConnectorWithPerm
         folder_path: str | None = None,
     ) -> None:
         self.batch_size = batch_size
-        self.folder_path = folder_path  # optional sub-folder filter, e.g. "/Documents"
+        self.folder_path = _normalize_folder_path(folder_path)
         self._access_token: str | None = None
         self._tenant_id: str | None = None