feat: release Agent Skill Store v0.2.0

[HYYH-code]

Summary

• use .agents as the shared Skill entry for Codex, Pi, and OpenCode
• add versioned package storage, project lockfiles, sync, doctor, migration, and Claude bridges
• enforce Junctions on Windows and symlinks on Unix with transactional rollback
• update documentation, web CLI guidance, CI matrices, E2E hosting, and release version to 0.2.0

Verification

• frontend: 12 tests, typecheck, production build
• .NET: Release build with 0 warnings and 0 errors
• tests: Core 73, Integration 72, CLI 147, E2E 13
• CLI publish: linux-x64, linux-arm64, osx-arm64, win-x64
• repository brand, path, secret, artifact, formatting, and script syntax scans

Constraint

Docker is not installed on the development machine; the required container build remains covered by CI.