docs(vrs): add thin Doctor contract

[myobie]

Summary

• Add only docs/vrs/02-doctor/requirements.md and docs/vrs/02-doctor/spec.md.
• State six Doctor requirements in ASD-STE100-style controlled English.
• Replace the dense check table with short field-first check groups.
• Keep Doctor as a diagnostic-only boundary. This PR adds no runtime behavior.
• Keep every source/evidence link and refresh each line range for current main.
• Keep all four open questions as questions, not requirements.

Doctor follows the root st2 vision. It does not define a separate health model.

Semantic map

• DOCTOR-R01: one selected catalog and host; no remote availability claim.
• DOCTOR-R02: zero only for health; each failure names its subject.
• DOCTOR-R03: no catalog, presence, runtime, reconcile, launch, stop, reap, repair, or materialization write.
• DOCTOR-R04: probes do not read caller input and have a fixed deadline.
• DOCTOR-R05: active local task liveness and presence.
• DOCTOR-R06: retired health requires complete task-record absence.
• The specification maps CLI inputs, six check groups, output/exit behavior, and the four unchanged product questions.

Size

File	Before	After
requirements.md	38 lines / 289 words	30 lines / 228 words
spec.md	55 lines / 380 words	60 lines / 338 words
Total	93 lines / 669 words	90 lines / 566 words

The specification uses five additional physical lines because the table became readable source-linked bullets. The total contract is three lines and 103 words smaller.

Current-main integration

• Merged live main ea58cda7d5ffd8a64cf157259425c6bd26549cb4 normally.
• Exact final head: 208577a1b8015e82117e74fa1755af5326cadd31.
• No force push, deploy, catalog mutation, runtime rollout, or reconcile occurred.

Verification at 208577a1b8015e82117e74fa1755af5326cadd31

• Local Markdown targets and line ranges: PASS
• cargo test --test doctor --test invariants --test native_only -- --test-threads=1: PASS (6 + 1 + 3)
• cargo test --doc --workspace: PASS
• cargo doc --workspace --no-deps: PASS with five unchanged live-main warnings
• git diff --check: PASS
• Hosted Nix: PASS — run 30637857695 / job 91179937995

This VRS head remains open and unmerged for Nathan's required exact-head review.

[myobie]

@schickling-assistant again, can we start thin with this too and work up from here?

[myobie]

ASD-STE100 rewrite complete at exact head 208577a1b8015e82117e74fa1755af5326cadd31. All six requirements, every source/evidence link, the diagnostic-only boundary, and all four open questions remain. Local link/docs/tests and hosted Nix run 30637857695 are green. Holding open and unmerged for Nathan's exact-head VRS review.