feat(rest-api): list all tasks for a site

[kunzhao-nv]

Problem

The REST API can list tasks for a Rack or Tray and retrieve an individual Task, but it cannot list every Task created in one Site. Operators need a site-wide view without enumerating inventory resources and merging results client-side.

Proposed API

Add GET /v2/org/{org}/nico/task with required siteId query parameter.

Support:

• activeOnly to restrict results to non-terminal Tasks
• includeReport to opt into execution reports
• pageNumber and pageSize pagination
• X-Pagination response metadata
• deterministic ordering by creation time descending and Task UUID descending before pagination

The endpoint should require Provider Admin access, validate Site ownership and Flow enablement, dispatch Flow ListTasks through the generic gRPC proxy, and update the OpenAPI contract and generated client/docs.