docs: clarify agent command UX

[baskduf]

Summary

• Reframe the command UX around user stages: First time, Daily work, and Maintenance
• Promote /harness adopt as the canonical first-time prompt-first adoption workflow
• Align Codex and Claude Code docs around doctor → adopt, review, and update/refresh
• Bump Agent Skills package refs/manifests to 0.1.15 for the command UX release
• Add decision memory and task-outcome evidence for the command UX change

Test Plan

• Added regression tests for README command-stage UX and Codex/Claude adopt command visibility
• python3 -m unittest discover -s tests — 202 tests passed, 2 skipped
• python3 -m py_compile scripts/apply_harness.py scripts/check_agent_skills_package.py scripts/check_docs_drift.py scripts/check_structure.py scripts/check_encoding_hygiene.py scripts/check_effectiveness_plan.py scripts/check_failure_memory.py scripts/check_decision_memory.py scripts/harness_doctor.py
• python3 scripts/check_agent_skills_package.py
• python3 scripts/check_docs_drift.py
• python3 scripts/check_structure.py
• python3 scripts/check_encoding_hygiene.py
• python3 scripts/check_effectiveness_plan.py
• python3 scripts/check_failure_memory.py
• python3 scripts/check_decision_memory.py
• python3 scripts/harness_doctor.py --target . — 100/100
• git diff --check

Release notes

• Prepares v0.1.15 in starter-kit docs/manifests. Tag after this PR and the marketplace sync PR are merged.

[baskduf]

Local approval note: I ran the documented validation successfully and consider this PR safe to merge. GitHub does not allow me to submit a formal approving review because this PR was opened by the same account (baskduf).