Add agency-health skill package

[codexbountylab]

Summary

• add skills/agency-health as a read-only agency case health assessment package
• emit degraded-health, needs-more-evidence, and needs-agent outcomes with routed intervention findings
• keep the package standalone so it passes both local and hosted registry publish paths

Verification

• cargo run --manifest-path crates/Cargo.toml -p runx-cli -- harness skills/agency-health --json
• cargo run --manifest-path crates/Cargo.toml -p runx-cli -- registry publish skills/agency-health/SKILL.md
• cargo run --manifest-path crates/Cargo.toml -p runx-cli -- registry publish skills/agency-health/SKILL.md --registry https://api.runx.ai

Harness result: passed, 3 cases, 0 assertion errors.
Local registry publish result: success.
Hosted registry publish result: success.
Hosted page: https://runx.ai/x/codexbountylab/agency-health@sha-dfef2e16f034

Frantic bounty: #106 agency-health.