docs: clarify enter and stay causes for parameter changes - #7959

What

Clarifies that cause follows the lifecycle of the route ID, including when path params or loaderDeps change. Adds the encoded parameter example from #7795 to show that a direct load uses enter, while navigation between values on an active route uses stay even when the match ID changes.

Closes #7795

Verification

• pnpm test:docs (244 Markdown files, no broken links)
• Prettier check for docs/router/guide/data-loading.md
• git diff --check

Summary by CodeRabbit

• Documentation
  • Clarified when data loaders run for active routes.
  • Explained that “stay” also applies when path parameters or loader dependencies change without changing the route.