feat(tui): add configurable home prompt sizing presets

[dmoliveira]

Closes #13929

Summary

• add tui.initial_prompt config with compact, medium, and large presets plus optional width_percent and height_percent overrides
• wire home-route prompt width and input max height to terminal-aware preset and override resolution
• include docs, config validation tests, and regenerated SDK/OpenAPI artifacts

Testing

• bun run typecheck (from packages/opencode)
• bun test test/config/config.test.ts -t "tui initial prompt" (from packages/opencode)
• bun run build (from packages/web)
• ./packages/sdk/js/script/build.ts
• bun script/generate.ts

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[dmoliveira]

Addressed ✅ Linked issue-first requirement by creating #13905 and updating the PR description with Closes #13905.

[dmoliveira]

Updated for compliance: opened replacement issue #13929 using the feature template and relinked this PR to Closes #13929.