docs(release): refresh post-0.8.7 roadmap

[limaronaldo]

Summary

• replace stale v0.8.7 release-prep status with current post-release state
• update the detector count from 19 to 20
• record SHIELD-020, local discovery, risk assessment, and isolated OpenClaw skill layouts
• identify release packaging/versioning as the next explicitly gated work

Why

docs/NEXT_STEPS.md still described v0.8.7 as unreleased and stopped at SHIELD-019. The live GitHub release is v0.8.7 (published June 15, 2026), while current main contains the subsequent architecture and implementation increments.

Impact

Documentation only. No product, API, output, policy, detector, build, or release mutation.

Validation

• verified live GitHub release and current origin/main history
• cross-checked rule registration and command implementation
• git diff --check

[limaronaldo]

Documentation review verdict: PASS — no findings.

Verified against live/current state:

• v0.8.7 is published (June 15, 2026)
• scanner registry includes SHIELD-001..020
• SHIELD-020 contextual composite flow is merged
• agentshield discover is implemented
• scan --experimental-risk is implemented as informational opt-in
• direct OpenClaw .agents/skills/<skill>/SKILL.md targets are merged
• release/tag mutation remains a separate explicit gate
• PR changes only docs/NEXT_STEPS.md