Replace Legacy Branch Protection with Repository Rulesets

[roblarsen]

Context

This repository receives an incredibly high volume of translation and typo-fix PRs. Relying on legacy Branch Protection rules restricts our ability to use modern automation (like auto-formatters, translation-sync bots, or labelers) because the standard GITHUB_TOKEN cannot bypass branch protection. Moving to Repository Rulesets fixes this.

Tasks

• Implement a new Repository Ruleset targeting the main branch.
• Configure standard rules: Require pull requests, status checks (markdown linting), and linear history.
• Configure "Bypass Actors" within the Ruleset to explicitly allow GitHub Actions and any designated formatting bots to commit/push directly.
• Disable the legacy Branch Protection rules on the main branch once the Ruleset is active.