Summary

• Adds POST /webhooks/slack endpoint that accepts pre-formatted markdown content and prints it directly on the receipt printer
• Supports inline images via ![alt](url) markdown syntax (downloaded and printed inline in content flow)
• Optional bearer token auth, header/footer/QR code toggles, and paper cut control
• Includes SKILL.md consumer spec with full API reference, supported markdown, receipt dimensions, and examples

New files

• src/papercut/platforms/slack/ — config, models, router (follows existing Linear platform pattern)
• SKILL.md — complete API spec for any consumer/agent to integrate with

Modified files

• src/papercut/core/printer.py — print_raw_receipt(), image download + inline rendering
• src/papercut/core/console.py — print_raw_console_preview() for dev/debug
• config.py — Slack provider config loading
• src/papercut/api.py — conditional Slack router registration
• papercut.toml / papercut-schema.json — [providers.slack] config section

Simplest usage

curl -X POST http://localhost:8000/webhooks/slack \
  -H "Content-Type: application/json" \
  -d '{"content": "# Hello\n\nThis is a **test** print."}'