fix(www): include showcase pages in sitemap

[zigzagdev]

Description

apps/www/app/sitemap.ts never imported showcaseSource, so the statically generated /showcase/[...slug] pages were missing from sitemap.xml while docs and blog pages were included.
This adds showcase pages to the sitemap using the same pattern as the existing docs/blog entries.

Changes

• Import showcaseSource from @/lib/source in apps/www/app/sitemap.ts
• Add showcaseSource.getPages() entries to the sitemap output (no lastModified, since the showcase frontmatter schema has no date field)

Motivation

/showcase/[...slug] pages are statically generated (generateStaticParams) and publicly linked from /showcase, but were excluded from sitemap.xml, so search engines had no sitemap-driven discovery path for them.
Verified via pnpm build: the generated sitemap.xml now contains all 26 /showcase/* URLs, matching the 26 files in content/showcase.

Breaking Changes

None.

Screenshots

N/A (sitemap XML output only)

Checklist

• pnpm check passes locally
• pnpm build passes locally
• pnpm build:registry was run and the generated files are committed (if you changed registry/ or config/site.ts — CI verifies this on every PR)
• PR title follows Conventional Commits (e.g., fix(www): include showcase pages in sitemap)

[vercel]

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[Yeom-JinHo]

Thanks @zigzagdev, but this one is intentional. I dropped the showcase entries in #1015 (52bd34c) because the /showcase/[slug] detail pages are too thin (a title and one card) to promote for indexing. They're still linked from /showcase, so crawlers can reach them.

Closing.