Community skills: search, pagination, and an "Add your skill" section

[kaankacar]

Before we announce the site more broadly and link it from the developer docs, the Community Built section on skills.stellar.org needs to handle that volume, and people need a documented way to get listed.

1. Search + pagination for community skills

• Simple search over the community cards. It must match the title and any part of the description, so searching "DEX" surfaces the Soroswap skill(an example) even though the word isn't in its title.
• Paginate the section so 20+ cards don't turn the landing page into an endless scroll.

Constraints (see site/CLAUDE.md):

• Card data must stay server-rendered in the static export. Search and pagination should be client-side filtering over cards already in the HTML, same pattern as the existing SkillsFilter island. No runtime fetching, no state libraries.
• /llms.txt is generated separately at build time and must keep listing every community skill regardless of what the UI shows. Search and pagination are for human eyes only.

2. "Add your skill" section

• Add a short section to the site explaining how to get listed: open a PR that adds an entry to ECOSYSTEM_CARDS in site/src/data/skills.ts (title, verb-led description, pathLabel, copyValue pointing at the skill's SKILL.md, category Ecosystem). Inline the snippet from site/CLAUDE.md so contributors don't have to dig for the format.

Done when

• Searching any word from a community skill's title or description finds it (case-insensitive)
• Community section paginates
• Every community skill still appears in the generated llms.txt
• All card data still visible in the server-rendered HTML
• "Add your skill" section is live and tells people to open a PR
• pnpm lint, pnpm lint:ts, and pnpm build pass