feat: make human-facing output concise

[BjRo]

Why

Closes #206. Darrow had no repository-wide plain-language contract, and several human-facing skill results buried the outcome or next action behind detail and process narration.

What changed

• Add result-first writing rules to repository guidance, the documentation quality contract, user guides, and six capability specifications.
• Revise discovery, explanation, readiness, review, verification, and skill-authoring output contracts for familiar language, progressive disclosure, and preserved evidence and safety fields.
• Move review and readiness next actions ahead of detail, tighten verification handoffs, add semantic communication evals, and bump both manifests for every changed plugin.
• Repair the discovery eval loophole test so semantic assertions remain semantic and give its shell loop a stable timeout under full-suite load.

Verification

• PASS: bun run lint; bun run lint:ts; bun run lint:shell; bun run typecheck.
• PASS: bun run check:decisions; bun run check:docs; bun run check:python; bun run check:python:inventory.
• PASS: bun test — 632 tests, 0 failures.
• PASS: all eight changed skills pass the bundled inspector.
• PASS: the eight focused eval definitions dry-prepare on Codex and Claude Code.
• Live focused trials passed on Codex for authoring, discovery, grilling, planning, visual explanation, readiness, review, and verification during development. Claude Code passed authoring, discovery, grilling, planning, visual explanation, and readiness.

Review notes

The riskiest changes are the fixed report ordering in darrow-review, the readiness result template, and the verification retained-report handoff. Deterministic renderer, composition, Python, and repository suites pass.

Two cross-host limitations remain visible in retained eval evidence: the Claude code-review presentation case has a longstanding zero-pass history because the candidate substitutes an ad hoc review for the artifact workflow, and verification reruns showed provider/backend lookup variance plus a concision-grader disagreement. The branch adds no migration, security, licensing, or external-state behavior.

Checklist

• I have read and followed CONTRIBUTING.md, including the contribution licensing terms.
• I added or updated the applicable invariant before implementation, or this change does not affect a capability invariant.
• I added or updated colocated evals, or this change does not affect skill behavior.
• I confirmed that each changed plugin remains self-contained, or this change does not affect plugin content.
• I ran bun run check:python, or this change does not affect registered Python packages or their repository quality infrastructure.