Prepare Planr v1.5.2 release candidate

[regenrek]

Summary

• prepare Planr v1.5.2 public release notes and README release-surface wording
• add release-candidate evidence at docs/release-candidates/planr-v1.5.2.md
• harden the Switchloom cross-product oracle used by the optional v0.2.1 dogfood handoff

Candidate evidence

• Candidate evidence document: docs/release-candidates/planr-v1.5.2.md at reviewed head e5832c40583451f96dd3cba87e2fb2569732524a
• Switchloom dogfood evidence section: Switchloom v0.2.1 Optional Dogfood Evidence at reviewed head e5832c40583451f96dd3cba87e2fb2569732524a
• Supporting local receipt provenance: /private/tmp/planr-switchloom-cross-product-QEvWps/oracle-receipt.json
• Fresh dogfood receipt SHA-256: c01f4b980977a15028f7a82cc6fc237aa50fb4b35310871ba3ad245ec1c699ee
• Public Switchloom package: switchloom@0.2.1, shasum e813283f54d0d64b5fd4835e17687aaaf3b0a6cb, integrity sha512-vUKHxYXHt7Sx7MkYQz5MRZ0Ll544iHoadHGCgvJPUYkpUzQWtzjt1o3xhyeQwExCA6tuLQ5vZnLPz+fO5uMiXg==

Verification

• scripts/ci-local.sh
• pnpm docs:content
• pnpm docs:typecheck
• pnpm docs:lint
• pnpm docs:build
• pnpm docs:verify-onboarding
• pnpm docs:verify-agent-recipes
• pnpm docs:verify-agent-journey
• pnpm docs:verify-agent-landing
• pnpm docs:verify-agent-markdown
• pnpm docs:verify-concepts
• pnpm docs:verify-reference
• pnpm docs:verify-maintenance
• pnpm docs:verify-release
• CARGO_NET_OFFLINE=true pnpm docs:verify-clean-install
• pnpm docs:verify-deployment
• PLANR_DOCS_URL=http://localhost:3099 pnpm docs:verify-shell
• scripts/build-release.sh
• scripts/security-local.sh
• cargo test --test routing_ownership
• python3 /Users/kregenrek/.agents/skills/gh-action-scan/scripts/run_zizmor_scan.py . --persona regular --min-severity medium --min-confidence medium
• python3 /Users/kregenrek/.agents/skills/gh-action-scan/scripts/run_zizmor_scan.py . --persona auditor --format json-v1 --output /tmp/planr-zizmor-auditor.json --allow-findings

Approval request

Please approve the exact release source and external actions before any release action is performed:

• Release source: PR Prepare Planr v1.5.2 release candidate #31 head e5832c4 on branch release-v1.5.2-scope
• External actions requiring approval: merge PR Prepare Planr v1.5.2 release candidate #31, create and push tag v1.5.2, create the GitHub Release, publish Planr v1.5.2 to npm, and update Homebrew

Release boundary

This PR is release preparation only. Do not merge, create or push tag v1.5.2, publish a GitHub Release, publish npm, or update Homebrew until explicit user approval names this exact release source and external actions.