Classify products by kind; pin single products to collections

Added

• Classify and filter products and sources by kind — platform, SDK, mobile, desktop, docs, integration, or tool — across the API and MCP server.
• Pin a single product to a collection instead of bringing its whole organization along.

Changed

• The catalog, search, and home page now hide organizations with no indexed releases by default, with an opt-in to show them.
• Boilerplate releases with no real content no longer get a misleading auto-generated summary.