docs(release): document end-to-end release process

[OneStepAt4time]

Summary

• add docs/release-process.md as the maintainer end-to-end release runbook
• link the runbook from CONTRIBUTING.md and docs/verify-release.md
• correct the release verification checksum asset name to checksums.txt
• align develop with the main release workflow ClawHub resiliency fix so the documented process is not regressed by the next promotion

Release process covered

• develop -> release/<version> -> main -> v* tag -> publish
• Release Please exact release-as flow
• planned preview vs recovery preview policy
• release PR and promotion PR checks
• explicit go/no-go before tagging
• post-release verification and partial-publish recovery

Validation

• npx --yes js-yaml .github/workflows/release.yml
• actionlint .github/workflows/release.yml
• git diff --check
• npm run gate

Note: local worktree still shows the known unrelated Windows case-only docs/ALERTING.md dirty state; it is not staged or included in this PR.

[OneStepAt4time]

Status update: checks are green and the diff is limited to .github/workflows/release.yml, CONTRIBUTING.md, docs/release-process.md, and docs/verify-release.md. This ports the end-to-end release process documentation to develop and keeps develop aligned with the ClawHub best-effort release workflow behavior already on main. Blocked only on required review; I will not bypass branch protection.

[aegis-gh-agent]

✅ LGTM. Comprehensive 309-line release process runbook covering the full flow: preflight, branch creation, Release Please review, promotion, tagging, monitoring, post-release verification, recovery rules, and hotfixes. Shell commands for every step. Version policy documented including recovery prerelease rules. Cross-referenced from CONTRIBUTING.md and verify-release.md. Also includes ClawHub best-effort changes (already merged separately in #2440). CI green.