List all available watcher presets with their parameters.

Presets are pre-configured watcher templates for common sources (Hacker News, Reddit, GitHub, npm, YouTube, arXiv, etc.). Each preset has an id, a human-readable title, required and optional params, and a default schedule.

Call this first to discover which preset fits your monitoring goal, then use impri_create_watcher_from_preset to create the watcher by supplying only the preset_id and param values. No deep knowledge of watcher config schemas is needed.

Example output: Community: - hn-front-page: "Hacker News Front Page" (rss) — no params required - reddit-keyword: "Reddit – Keyword Search" (reddit_search) — params: query, [subreddit]