Add current Xquik Skill and fix seed build failures

[kriptoburak]

Summary

• Add the current Xquik x-twitter-scraper Skill to the SkillX seed catalog.
• Cover REST, remote MCP, SDKs, search, exports, monitoring, webhooks, and approval-gated publishing.
• Use the public Skill source and current install command.
• Keep read-only defaults, explicit approval gates, untrusted-content handling, and credential boundaries.
• Remove invented install and rating metrics from the new seed entry.
• Make seed-build failures return a nonzero process status.
• Add regression coverage for unreadable seed data.

Independent Fix

build-seed-data.mjs previously used main().catch(console.error). Read, parse, or write failures printed an error but left the process exit status at 0. Automation could therefore accept a failed seed build. The script now sets process.exitCode = 1, and the regression test executes an isolated copy without seed-data.json to verify the failure contract.

Validation

• pnpm install --frozen-lockfile
• pnpm test (39 tests pass)
• pnpm build
• node --check scripts/build-seed-data.mjs
• node --check scripts/build-seed-data.test.mjs
• node scripts/build-seed-data.mjs
• Parsed scripts/seed-data.json and verified exactly 1 Xquik row.
• Verified the public Skill source, MCP endpoint, and OpenAPI endpoint.
• git diff --check

pnpm typecheck still reports pre-existing errors in unchanged app files. This PR adds no TypeScript application code and introduces no new typecheck error.

[kriptoburak]

@codex review

Please review the refreshed Xquik seed entry, removal of synthetic engagement metrics, and the independent nonzero-exit fix for failed seed builds. Commit 060a8e5 passes all 39 tests and the production build.