feat(cli): add skill gateway to install and sync skills across agents (#1442)

[Adityakk9031]

Summary

Implements the Skill Gateway for Executor as requested in #1442.

This introduces a central skill management store and multi-agent sync engine in Executor CLI (executor skills ...), allowing developers to install agent skills once (from git repos, local directories, or URLs) and sync them across all connected AI coding assistants (Claude Code, Codex, Antigravity/Gemini CLI, Cursor, Windsurf), with workspace/global scopes and enable/disable toggling to prevent context bloat.

Features

1. Central Skill Store:
   • Manages skills in .executor/skills/<name>/ (workspace) or ~/.executor/skills/<name>/ (--global).
   • Tracks installed skills, source type, checksums, enabled state, and synced targets in skills-lock.json.
2. Multi-Agent Sync:
   • Auto-detects supported agent directories:
     • Claude Code (.claude/skills/, ~/.claude/skills/)
     • Codex (.codex/skills/, ~/.codex/skills/)
     • Antigravity / Gemini (.agents/skills/, ~/.gemini/antigravity/skills/)
     • Cursor (.cursor/skills/, ~/.cursor/skills/)
     • Windsurf (.windsurf/skills/, ~/.windsurf/skills/)
   • Synchronizes skill folders, markdown instructions, helper scripts, and assets.
3. Skill Toggling:
   • executor skills toggle <name> enable|disable dynamically activates or deactivates skills without uninstalling them, preventing context bloat across different stacks.
4. CLI Commands:
   • executor skills list [--global]
   • executor skills add <source> [--name <name>] [--global]
   • executor skills remove <name> [--global]
   • executor skills toggle <name> enable|disable [--global]
   • executor skills sync [--global]

Verification

• Added test suite apps/cli/src/skills-gateway.test.ts covering skill installation, metadata extraction, lockfile management, multi-agent detection, skill toggling, and removal.
• All unit tests pass.
• tsgo --noEmit on apps/cli passes cleanly with 0 errors.
• oxlint and format checks pass with 0 errors.

Fixes #1442

[Adityakk9031]

@RhysSullivan have a look