Unify CLI status and doctor graph health semantics

[jununfly]

Summary

• Add a shared graph-health classification contract for healthy, degraded, stale, failed, unavailable, and corrupted.
• Expose that health summary through zcodegraph status --json and the human-readable zcodegraph status first screen.
• Align zcodegraph doctor bundle summaries and missing-source-record prompts with the same graph-health language.
• Document status as the graph trust check in README and record the user-facing change in CHANGELOG.

Roadmap

• Roadmap id: cli-status-doctor-semantics
• Closeout status: complete
• Process roadmap files were deleted in the closeout commit after durable decisions moved into README/CHANGELOG and tests.
• Deferred follow-up: [cli-status-doctor-semantics] 1-3-2 corrupted diagnostic bundle v2 #671 for a future corrupted-DB doctor bundle path that does not open the malformed DB.

Verification

• npm run build
• npx vitest run __tests__/graph-health.test.ts __tests__/status-json.test.ts __tests__/rust-hybrid-doctor.test.ts
• git diff --check

Human Gates

• Confirmed shared user promise: status answers whether the graph can be trusted, doctor packages diagnostics for maintainers, and init/index give immediate post-run feedback.
• Confirmed corrupted DB behavior: status prints recovery commands and stays non-destructive; doctor corrupted bundle v2 is deferred.
• Confirmed continuous roadmap execution constraint: run leaf-by-leaf until a Human Gate, failed gate, scope expansion, delete/publish/merge boundary, or closeout boundary.