feat: multi-CLI installer with registry pattern (7 platforms)

[gabelul]

Summary

• Refactors bin/stitch-kit.mjs from hardcoded 2-platform logic to a registry-driven architecture supporting 7 CLI tools
• Each platform is a declarative config object — adding a new client = adding one object to the CLIENTS array
• Generic functions (installClient, uninstallClient, statusClient) iterate the registry instead of per-platform if/else

Supported Platforms

Platform	Agent	Skills	MCP Config	Notes
Claude Code	✓	plugin	JSON mcpServers	Plugin recommendation hook
Codex CLI	✓	✓	TOML mcp_servers	—
Cursor	—	—	JSON mcpServers	—
VS Code	—	—	JSON servers + type: http	Extra Accept header
OpenCode	✓	✓	JSON mcp + type: remote	enabled: true flag
Crush	—	✓	JSON mcp + type: http	—
Gemini CLI	—	—	—	Extension install, no config file

Key Design Decisions

• TOML stays as special case in installMcp() — only Codex uses it, no parser dependency needed
• Gemini CLI uses isExtensionBased: true + mcp: null to cleanly skip MCP logic
• API key prompted once, shared across all detected platforms
• MCP config left in place on uninstall — user may want to keep it

Test plan

• npx @booplex/stitch-kit status — shows all 7 platforms (detected/not-detected)
• npx @booplex/stitch-kit --help — lists all platforms with feature summary
• npx @booplex/stitch-kit -v — version output works
• Test install with API key on fresh machine
• Verify JSON output matches official Stitch docs for each platform
• Test uninstall removes only what was installed