test: add colocated core component acceptance suite

[kvinwang]

Summary

This PR adds the core-component acceptance suite and organizes the complete suite directly under test-suites/ so specifications, automation, fixtures, inventories, manifests, and retained audit evidence have one clear home.

• Adds the deterministic dstack-test runner, dashboard, registry validation, fixture providers, and component harnesses.
• Adds 358 acceptance cases covering guest OS, VMM, KMS, gateway, verifier, and cross-component integration behavior.
• Colocates single-case entrypoints with their case.md specifications as run.py, run.sh, or run.cjs.
• Keeps multi-case and location-sensitive harnesses in shared/automation/.
• Distributes metadata across suite, chapter, section, and case directories; the runner discovers cases in directory-name order.
• Uses each case-local metadata.json as the authoritative case-to-entrypoint binding.
• Keeps fixture providers and images under shared/fixtures/, inventories under catalog/, environment manifests under manifests/, and retained historical evidence under audit/.
• Adds suite authoring, execution, reporting, and methodology documentation.
• Excludes product/runtime changes and source-local unit tests; those changes were split into dedicated PRs.

Layout

test-suites/
├── runner/
├── cases/
├── shared/
│   ├── automation/
│   └── fixtures/
├── catalog/
├── manifests/
└── audit/

Separation invariant

The PR targets next. Its changed paths are limited to:

• REUSE.toml
• docs/testing/**
• test-suites/**

There are no product/runtime or source-local test changes under dstack/** or os/**.

Verification

• Registry: 357 scripted / 357 promoted / 0 findings (358 total cases)
• Runner unit tests: 37 passed
• prek run --all-files: passed
• reuse lint: passed
• git diff --check origin/next...HEAD: passed

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