Trim harness docs and state templates

[devRonPark]

Summary

• Trimmed harness docs down to the active solo-builder path.
• Removed stale task/run artifacts from the default .harness surface.
• Simplified Claude/Codex command wrappers, CI comments, setup docs, GitHub docs, and planning defaults.

Verification

• python3 scripts/validate_tasks.py
• python3 scripts/sync_plans.py --check
• python3 -m unittest discover -s tests -q
• python3 scripts/validate_tasks.py --root templates/skeleton
• python3 scripts/sync_plans.py --root templates/skeleton --check
• bash -n init.sh
• bash -n scripts/setup-plugins.sh
• node --check scripts/merge-settings.mjs

Acceptance evidence

No single task ID was targeted; this is a harness YAGNI trim. Acceptance evidence is the verification list above plus preservation of existing completed-task grep checks for README, BLUEPRINT, GitHub branch protection, quality gates, and docs/templates paths.

Residual risk

• Large deletion set: mainly historical .harness task/run artifacts and optional docs. Review should focus on whether any deleted doc is still needed as user-facing default guidance.
• Existing PR remains draft for review.