perf: make data size calculation async for disable/uninstall responses

[yasinBursali]

Context

The _get_service_data_info() helper (added in #812) calls dir_size_gb() synchronously during disable/uninstall API responses. dir_size_gb() does a full recursive rglob("*") scan which could take several seconds on large data directories (e.g., ComfyUI models with tens of GB and thousands of files).

Problem

The disable/uninstall response is delayed by the directory scan. For a 50GB data directory with 10K+ files, this could add 2-5 seconds to what should be a fast operation.

Proposed Solution

Options (pick one):

1. Background annotation: Return the disable/uninstall response immediately, fire off an async task to compute data_info, and make it available via a separate GET /api/extensions/{id}/data-info endpoint
2. Cached size: Pre-compute and cache directory sizes periodically (e.g., every 60s), return the cached value in disable/uninstall responses
3. Opt-in parameter: Add ?include_data_info=true query param, skip the scan by default

Priority

Low — affects UX only for services with very large data directories. The current synchronous approach works correctly for all services.

[yasinBursali]

Closing — issue filed on wrong repo.