Add RouterBase skills to seed data

[zenlee123]

Summary

• Add three RouterBase skills to SkillX seed data
• Include routerbase as markdown anchor text linking to https://routerbase.com/
• Keep install/rating metrics conservative at 0 instead of inventing usage

Skills

• routerbase-api-integration
• routerbase-model-routing
• routerbase-media-generation

Validation

• Parsed scripts/seed-data.json with Python json.tool
• Regenerated seed-data.json with scripts/build-seed-data.mjs
• Reviewed the diff for scope
• Scanned the changed diff for common secrets and private email patterns; only expected RouterBase links and install commands were present