feat(nextcloud): trigger endpoint for bulk migrations

[rezk2ll]

Summary

Adds POST /remote/nextcloud/migration to start a Nextcloud-to-Cozy bulk migration from the Settings UI.

The endpoint probes the supplied credentials against the Nextcloud OCS user_status endpoint, upserts an io.cozy.accounts document with the resolved WebDAV user ID, creates an io.cozy.nextcloud.migrations tracking document in pending state, and publishes a nextcloud.migration.requested command to the new migration RabbitMQ exchange.

A separate migration service consumes the command and drives the existing /remote/nextcloud/:account/* routes to perform the transfer, writing progress back to the tracking document.

The Settings UI monitors the document in real time to display progress. Only one migration can be in flight per instance; failed migrations do not block new attempts.

API

POST /remote/nextcloud/migration (requires POST io.cozy.nextcloud.migrations)

{
  "nextcloud_url": "https://nextcloud.example.com",
  "nextcloud_login": "alice",
  "nextcloud_app_password": "xxxxx-xxxxx-xxxxx-xxxxx-xxxxx",
  "source_path": "/"
}

source_path is optional and defaults to /. The password should be a Nextcloud app password.

201 Created

{
  "data": {
    "id": "d4e5f6a7b8c94d0ea1b2c3d4e5f6a7b8",
    "type": "io.cozy.nextcloud.migrations",
    "attributes": {
      "status": "pending",
      "target_dir": "/Nextcloud",
      "progress": {
        "files_imported": 0,
        "files_total": 0,
        "bytes_imported": 0,
        "bytes_total": 0
      },
      "errors": [],
      "skipped": [],
      "started_at": null,
      "finished_at": null
    }
  }
}

Error responses

Code	When
401 Unauthorized	The Nextcloud server rejected the supplied credentials
409 Conflict	A pending or running migration already exists for this instance
500 Internal Server Error	Conflict check, account upsert, or tracking document creation failed
502 Bad Gateway	The Nextcloud instance is unreachable
503 Service Unavailable	RabbitMQ publish failed; the tracking document is marked failed before returning

RabbitMQ contract

Exchange migration, routing key nextcloud.migration.requested. Payload (the consumer is responsible for declaring its queue and binding):

{
  "migrationId": "d4e5f6a7b8c94d0ea1b2c3d4e5f6a7b8",
  "workplaceFqdn": "alice.cozy.example.com",
  "accountId": "a1b2c3d4e5f6",
  "sourcePath": "/",
  "timestamp": 1712563200
}

Credentials are never in the payload; they live in the io.cozy.accounts document referenced by accountId. MessageID is set to the migration ID for cross-system tracing.