Add deterministic top-level panel ordering

[yannglt]

Summary

• add an optional order option to panel APIs across React, Solid, Svelte, and Vue
• render explicitly ordered panels first, preserving registration order for ties and unordered panels
• document the option and cover store ordering behavior

Validation

• npm test
• npm run typecheck
• npm run build

npm run typecheck retains the repository’s existing Svelte warnings; it reports zero errors.