Add MS Graph write endpoints for drive items

[dschmidt]

Libre Graph specs reads on /drives/{id}/items/{id} (GET), a narrowly-scoped PATCH (only @UI.Hidden), DELETE (share-jail unmount only), and GET /content (#38, merged). Several MS Graph write endpoints are missing or incomplete. Consumers fall back to WebDAV for write ops and pay an extra Graph round-trip per path segment to resolve the resulting driveItem (concrete example: opencloud-eu/n8n-nodes-opencloud#11).

Endpoints needed for MS Graph parity:

Endpoint	Purpose	Spec	Server impl
POST /items/{item-id}/children (non-root)	create folder / file shell at arbitrary parent	needed (draft in #42)	needed
PUT /items/{item-id}/content	one-shot small-file upload	needed	needed
POST /items/{item-id}/copy	copy item	needed	needed
PATCH /items/{item-id} (rename / move)	accept name and parentReference beyond @UI.Hidden	needed (spec line 1231 locks body)	needed
DELETE /items/{item-id} (normal drive items)	recycle / permanently delete non-share-jail items	already broad enough (line 1280 describes recycle-bin behavior; example at line 1298 uses a share-jail-shaped id and could be supplemented with a normal example)	needed
GET /items/{item-id}/children (non-root)	list children of a folder at arbitrary parent	needed (draft in #43)	already exists (GetDriveItemChildren)

Notes on individual endpoints:

• PUT /content: returns the uploaded driveItem (201 + driveItem), so clients can drop the post-upload resolve walk. feat: Add @microsoft.graph.downloadUrl annotation and /content endpoi… #38 covered the download direction.
• POST /copy: MS Graph returns 202 Accepted + monitor URL (no body); a synchronous variant for fast copies (body containing the destination driveItem) would let clients skip the monitor.
• PATCH /items/{item-id}: name and parentReference combinable in one request; response is the updated driveItem. Cross-storage moves are inherently non-instant and should be rejected with a structured error, matching today's WebDAV 502.

Related (in flight):

• feat(graph): add MS Graph colon-syntax path lookup middleware opencloud#2688: server-side colon-path middleware.