docs: fill remaining VDR onboarding and troubleshooting gaps

[miyoungc]

Description

The installation Quick Start does not explain how to verify the package or obtain repository examples. The remaining VDR 0.20 gaps also leave GLiNER hard to discover and omit deployment troubleshooting and self-check model evaluation guidance.

Add installation verification and version-aligned example checkout instructions, a GLiNER card on the Tutorials landing page, troubleshooting for the five reported deployment symptoms, and a labeled self-check evaluation procedure. The GLiNER card preserves the existing guide URL; final navigation/relocation acceptance remains open under NGUARD-697.

Related Issue(s)

Tracking uses the existing Jira tickets:

• NGUARD-679: post-install verification
• NGUARD-682: obtaining repository examples
• NGUARD-697: GLiNER tutorial discovery
• NGUARD-698: deployment troubleshooting
• NGUARD-701: self-check model evaluation

Verification

• Pre-commit passed on all four changed MDX files, including ty; structured review found no actionable defects.
• Installation import/version and CLI help checks passed. All four existing GLiNER configurations parsed without model calls, and the Python example compiled.
• 163 focused output-parser, content-safety-flow, and GLiNER tests passed through make test WORKERS=1, with live-provider keys unset.
• Cached-reference Fern check: 0 errors, 1 warning. Fresh SDK generation and remote redirect comparison are blocked by Fern organization-access HTTP 403. Cached latest SDK references came from the pre-update clone.
• git diff --check passed. Live model/server qualification was not performed.

AI Assistance

• AI tools were used: Codex prepared and validated these documentation edits and performed structured review. Human review remains pending while this PR is draft.

Checklist

• I've read the contribution guidelines and AI policy.
• My PR title follows the project commit convention.
• I've updated the documentation.
• I've recorded verification and its limits.
• I did not update generated changelog files.
• Human and automated review comments addressed before maintainer review.

Current CI limitation: Check Fern docs fails before documentation validation because the fork workflow has no FERN_TOKEN; SDK generation reports that authentication is required. Other checks are still running.

[miyoungc]

Superseded by #2452, which uses the branch in NVIDIA-NeMo/Guardrails as requested.