ci: enable develop branch workflow

[roger-gan]

Description

Enable the two-branch development and release workflow after trusted policy validators have been bootstrapped into both main and develop. Add enforced PR routing, metadata validation, TypeScript CI, validator tests, branch documentation, and develop-based Changesets configuration.

This PR does not remove or modify the root legacy archive.

Tests

• sh scripts/check_branch_policy.test.sh
• node --test scripts/check_pr_metadata.test.mjs
• pnpm format:check from typescript
• workflow YAML syntax validation
• git diff --check

Branch route

• Normal development targets develop
• Only release or hotfix branches target main

Checklist

• I have formatted and linted my code
• All new and existing relevant tests pass
• This PR does not require a Changeset
• My commits are signed