fix: address PR review feedback for Collectives support

- Validate OCS envelope status before unwrapping data (raise OCSError on
  statuscode >= 400)
- Fix test data: filePath should be "" for root-level pages, not filename
- Catch specific exceptions (HTTPStatusError, OSError) instead of bare
  Exception in WebDAV content fetch, include error in log message
- Return updated resource data from update_collective, move_page, and
  set_page_emoji instead of discarding API responses
- Fix create_page docstring to mention collectivePath/filePath/fileName
- Remove unused additional_headers parameter from _get_ocs_headers
- Add unit test for OCS error status validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/client/collectives/test_collectives_api.py

@@ -3,7 +3,7 @@
 import httpx
 import pytest
 
-from nextcloud_mcp_server.client.collectives import CollectivesClient
+from nextcloud_mcp_server.client.collectives import CollectivesClient, OCSError
 from tests.client.conftest import create_mock_response
 
 pytestmark = pytest.mark.unit
@@ -46,7 +46,7 @@ def _sample_page(
         "title": title,
         "emoji": None,
         "fileName": f"{title}.md",
-        "filePath": f"{title}.md",
+        "filePath": "",
         "collectivePath": collective_path,
         "parentId": parent_id,
         "timestamp": 1700000000,
@@ -327,6 +327,28 @@ async def test_restore_page(mocker):
 # --- Error Handling ---
 
 
+async def test_ocs_error_status_raises(mocker):
+    """Test that OCS envelope with error statuscode raises OCSError."""
+    mock_response = create_mock_response(
+        status_code=200,
+        json_data={
+            "ocs": {
+                "meta": {
+                    "status": "failure",
+                    "statuscode": 403,
+                    "message": "Not permitted",
+                },
+                "data": {},
+            }
+        },
+    )
+    mocker.patch.object(CollectivesClient, "_make_request", return_value=mock_response)
+
+    client = CollectivesClient(mocker.AsyncMock(spec=httpx.AsyncClient), "testuser")
+    with pytest.raises(OCSError, match="Not permitted"):
+        await client.get_collectives()
+
+
 async def test_get_collectives_403(mocker):
     """Test 403 response raises HTTPStatusError."""
     mock_response = create_mock_response(