feat: add NX workspace fixtures and documentation

[Demiserular]

I added NX workspace fixtures and documentation to demonstrate CVE Lite CLI compatibility with NX integrated and package-based monorepo configurations, including a fixture that documents the known gap in mixed scenario handling.

Why this change

CVE Lite CLI needed verified NX workspace examples and documentation to help users understand how to scan NX monorepos. Testing revealed a known gap in mixed scenarios (root lockfile + nested lockfiles) that needed to be documented with workarounds.

What changed

• Added examples/nx-integrated fixture for NX integrated repos (single root lockfile)
• Added examples/nx-package-based fixture for NX package-based repos (per-project lockfiles under apps/ and libs/)
• Added examples/nx-mixed fixture demonstrating mixed scenario gap with README documenting the workaround
• Added website/docs/nx-workspaces.md with NX scanning guide and recommended command cve-lite . --search-depth 4
• Updated examples/readme.md with all three NX fixtures in the table and usage commands

Validation

Tested all three fixtures:

• nx-integrated: Successfully scans root lockfile and finds vulnerable axios@0.19.0
• nx-package-based: With --search-depth 4, discovers both nested lockfiles, scans independently, labels findings by folder path, provides project-specific fix commands
• nx-mixed: Confirms documented gap - only root lockfile scanned, nested lockfile not discovered (expected behavior)

User-facing impact

Does this change:

• affect scanning behavior
• affect output formatting
• affect JSON output
• affect docs only

Notes

Fixes #688
Scope: Fixtures and docs only. No code changes for mixed scenario handling (out of scope - will be handled separately using these fixtures for testing). The mixed scenario gap is documented in both the docs and the fixture README with workarounds provided.