docs: update textarea component page

[snoopuppy582]

Summary

• Add Textarea landing demos for default, error, disabled, and custom color states.
• Replace the Textarea API placeholder with a props table based on the current component props.
• Expand the component intro sentence to clarify common multi-line input use cases.

Related Issue

• Closes Update Textarea landing page #560

Tests

• bun x eslint apps/landing/src/app/(detail)/components/[component]/textarea/Api.mdx apps/landing/src/app/(detail)/components/[component]/textarea/index.mdx apps/landing/src/app/(detail)/components/[component]/textarea/demo/1_Default.tsx apps/landing/src/app/(detail)/components/[component]/textarea/demo/2_Error.tsx apps/landing/src/app/(detail)/components/[component]/textarea/demo/3_Disabled.tsx apps/landing/src/app/(detail)/components/[component]/textarea/demo/4_Colors.tsx
• bun run --filter landing lint
• bun run build
• Pre-commit lint/Rust coverage portion: passed through cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, eslint, and cargo tarpaulin --out xml --out stdout --all-targets --engine llvm with 97.75% coverage.

Notes

• bun run build:landing is currently blocked locally before the page is loaded by packages/next-plugin/dist/index.cjs raising ReferenceError: t is not defined from the generated build output.
• The full pre-commit bun test step is also blocked locally by generated packages/plugin-utils/dist/index.mjs exports such as u not being declared. The changed Textarea docs and demos pass the targeted landing lint checks above.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.