feat: add SkillHub expert market

[Pandakingxbc]

Summary

• Add a SkillHub-backed Expert Market alongside the existing featured expert list.
• Cache SkillHub skillsets as expert templates with manifest, workflow prompt, and skills.
• Generate bilingual welcome metadata and 6-9 quick prompts through a constrained internal manifest-generation skill, with deterministic fallback behavior.
• Add frontend market browsing, detail drawer, create flow, and quick prompt prefill behavior.

Validation

• make lint
• make all
• cd dashboard && npx tsc --noEmit
• cd dashboard && npx eslint src/pages/Chat/index.tsx src/pages/Experts/index.tsx src/pages/Experts/components/ExpertMarketTab.tsx src/pages/Experts/components/iconForName.tsx src/api/modules/expertMarket.ts --max-warnings=0
• make build-frontend

make all result: 1209 passed, 3 skipped, 11 deselected.

Notes

• The implementation is based on GitHub main rather than the internal WOA history, because the two repositories do not share a merge base.
• Generated src/octop/dashboard build artifacts are ignored by GitHub main and are not included in this PR.