Add unauthenticated /ping health endpoint for TrueNAS

[lzinga]

Summary

Adds a lightweight /ping endpoint at the root URL for use as a Docker/TrueNAS liveness probe. This matches the
convention used by Sonarr, Radarr, Lidarr, and other *arr apps, where TrueNAS app catalog templates call curl /ping for health checks.

Changes

Added

• GET /ping endpoint in SystemController — returns {"status":"OK"} with no authentication required
• <remarks> XML doc explaining why the route uses a leading / to override the controller prefix
• Integration tests for /ping (auth disabled + auth enabled scenarios)

Testing

• 2 integration tests in PingEndpointTests.cs:
  • Ping_Returns200_WhenAuthDisabled — verifies 200 OK without auth
  • Ping_Returns200_WhenAuthEnabled_WithoutCredentials — verifies [AllowAnonymous] bypasses auth middleware
• Both pass against ListenarrWebApplicationFactory
• Verified Sonarr's TrueNAS template uses healthcheck.set_test("curl", {"path": "/ping"}) at root

Notes

• The leading / in [HttpGet("/ping")] is intentional — it overrides the controller's api/v{version}/system
  prefix so the endpoint lives at the root, matching the *arr convention

Follow-up: TrueNAS App Catalog Submission

Once this PR is approved and merged, the next step is to submit Listenarr to the TrueNAS Apps
Catalog:

1. Fork truenas/apps into the Listenarrs org
2. Create the app definition at ix-dev/community/listenarr/ modeled after Sonarr's
   definition, which includes:
   • app.yaml — metadata (name, version, categories, icon, screenshots, maintainers, run_as_context)
   • item.yaml — catalog entry (categories, icon_url, tags)
   • ix_values.yaml — default image config (Docker image repo + tag)
   • questions.yaml — user config schema (port, storage mounts, env vars, resources)
   • templates/docker-compose.yaml — Jinja2 template with c1.healthcheck.set_test("curl", {"port": ..., "path": "/ping"})
   • templates/test_values/basic-values.yaml — CI test scenario (required)
   • README.md — short app description
3. Publish a Docker image (e.g., ghcr.io/listenarrs/listenarr) — required by ix_values.yaml
4. Host icon + screenshots on a public URL for app.yaml
5. Submit a PR to truenas/apps targeting the community train
6. Per TrueNAS CONTRIBUTIONS.md: open an issue
   first, run python .github/scripts/ci.py locally to validate, and open a draft PR early for maintainer feedback

[therobbiedavis]

Again some minor changes

[therobbiedavis]

@lzinga There are a couple non-blockers, so approving for now. If you want to address the non-blockers, feel free, and i'll re-review.

[therobbiedavis]

The rest of the test suite uses "false" instead of "Disabled". It returns false here only because it falls through the allowlist same as any other unknown string. Can you change is to false to be consistent and explicit?

[therobbiedavis]

I think we should also add a test case for the new [HttpHead("/ping")]. Which in that case it might be worth looking at going ahead and creating a private helper to make the test fixture setups easier.