get services from API, removing sidecar requirement (#772)

* get services from API, removing sidecar requirement

Signed-off-by: Matthias Bertschy <matthias.bertschy@gmail.com>

* fix: add timeout and file-based fallback to LoadServiceURLs

- Bound HTTP service discovery to 10 s so a slow/unreachable API
  cannot stall node-agent startup; failure is handled gracefully by
  the existing nil-check at the call site.
- Restore SERVICES env var / /etc/config/services.json fallback
  (using ServiceDiscoveryFileV3) so sidecar deployments retain
  scan-failure reporting without requiring migration to API_URL.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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Signed-off-by: Matthias Bertschy <matthias.bertschy@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>