feat: expose root help formatter

[floze-the-genius]

Summary

• make Help.formatRoot() a public API for callers that need to compose or extend root help
• remove the TypeScript suppression from the existing root-help test so visibility regressions fail compilation
• preserve the existing root help output and runtime behavior

Validation

• npx --yes yarn@1.22.22 mocha --forbid-only test/help/format-root.test.ts (5 passing)
• npx --yes yarn@1.22.22 compile --noEmit
• npx --yes yarn@1.22.22 eslint src/help/index.ts test/help/format-root.test.ts
• npx --yes yarn@1.22.22 test (821 passing; full lint, build, and circular-dependency check also passed; 8 pre-existing lint warnings outside this diff)
• npm pack --dry-run --json --ignore-scripts (163 files)

Closes #1284

AI disclosure

This contribution was implemented with assistance from OpenAI Codex. The scope, diff, and validation results are documented above.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @floze-the-genius to sign the Salesforce Inc. Contributor License Agreement.

[jfeingold35]

@floze-the-genius , I'll give this a review and let you know if anything needs to change before we can merge. In the meantime, can you please sign the CLA so we can merge it once it's ready? Thanks!