docs(mini-apps): multiple pages contain TODO stubs with no content

## Bug

Several Mini Apps documentation pages contain only TODO comments with no actual content, making them unhelpful for developers.

## Affected Pages

1. `docs/mini-apps/troubleshooting/error-handling.mdx` — `TODO: Provide guidance on handling errors from hooks, network issues, and manifest/metadata failures.`
2. `docs/mini-apps/quality-and-publishing/overview.mdx` — `TODO: Write end-to-end guidance for becoming Featured`
3. `docs/mini-apps/quality-and-publishing/submission-guidelines.mdx` — `TODO: Define required assets (icons, hero, screenshots), URLs, manifest checks`
4. `docs/mini-apps/quality-and-publishing/quality-bar.mdx` — `TODO: Draft the full Quality Bar article`

## Impact

Developers visiting these pages find no useful content, which harms the documentation experience.

## Steps to Reproduce

1. Visit any of the affected pages on docs.base.org
2. See only a TODO comment with no content