feat: Agent Skills Marketplace (Bounty #856)

[508704820]

Builds a marketplace where developers can publish, discover, and install AI agent skills (plugins/extensions for autonomous agents).

Skill Publishing

AgentSkill Model:

• Name, description, version, author
• 12 categories: search, code_generation, code_review, testing, deployment, security, documentation, data_analysis, communication, memory, orchestration, custom
• 5 compatibility targets: openclaw, claude_code, cursor, copilot, generic
• Tags, readme, install_command
• Price in $FNDRY (0 = free)
• Version history tracking

CRUD:

• POST /api/skills — Publish (duplicate check per author)
• GET /api/skills — Search with filters
• GET /api/skills/{id} — Get details
• POST /api/skills/{id}/install — Record installation
• POST /api/skills/{id}/rate — Rate 1-5 stars

Discovery & Search

• Full-text search (name, description, tags)
• Filter by category, compatibility, tags
• Free-only filter
• 4 sort modes: popular, rating, newest, installs

Rating System

• 1-5 star scale with comments
• One rating per user (update on re-rate)
• Auto-calculated average rating
• Rating count display

Install Tracking

• Downloads + installs counters
• Install command returned on install
• Version tracking for updates

Stats Dashboard

• GET /api/skills/stats/summary
• Total skills, downloads, installs
• Free vs paid breakdown
• By category and compatibility
• Top 10 skills by installs

Acceptance Criteria

• Publish and discover agent skills (12 categories + full-text search + 4 sort modes)
• Install and rate skills (install tracking + 5-star rating + version history)
• Marketplace with categories and ratings (free/paid pricing + stats dashboard)

Closes #856

Wallet: Lt9nERv6VHsojw15LpFeiaabuphAggzfLF9sM9UXRrZ