chore: remove outdated docs and planning files (#54)

Remove obsolete documentation:
- docs/features/*.md - Old ADR planning docs from March 2025, all implemented
- docs/mcp-example-clients.md - Copy-pasted MCP docs, not project-specific
- docs/mcp-js-readme.md - Copy-pasted MCP SDK readme, not needed

Keep:
- docs/coolify-openapi.yaml - Coolify API reference
- docs/openapi-chunks/ - Used by OpenAPI drift detection workflow

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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: StuMason