enhance(dev-backlog): mark spec lint and doctor checks as structural only

[sungjunlee]

Context

component-lint and capabilities-doctor are useful structural checks, but their green output can be misread as acceptance coverage. They do not prove that task AC, relay Done Criteria, or capability predicates are covered.

Desired change

Make structural checks explicit about what they do and do not assess.

Possible changes:

• include coverage: not_assessed or structural_only: true in JSON output
• add human-readable wording such as "routing handle validation only" or "capability spec hygiene only"
• enrich component-lint counts with routed/unrouted sprint counts so successful output does not imply every sprint is capability-routed

Acceptance Criteria

• capabilities-doctor.js --json communicates that acceptance coverage is not assessed.
• component-lint.js --json communicates that it validates routing handles, not task/capability coverage.
• component-lint reports checked/routed/unrouted sprint counts, including active vs legacy where practical.
• CLI text output avoids language that could be read as coverage approval.
• Tests cover the new output fields and wording.

[coderabbitai]

🔗 Related PRs

#110 - docs: dogfood spec/capabilities.md for dev-backlog itself (#105) [merged]

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[sungjunlee]

Scope note: this is adjacent hygiene for dev-backlog helper scripts, not part of the first spec-* documentation batch. It can follow #183-#186; its purpose is only to prevent structural checks from being mistaken for AC or capability coverage.