feat: add you.com search provider

[mouse-value-add]

Hi @longevityboris — thanks for building search-cli. I picked this repo because it already has a clean provider abstraction, active maintenance, and strong agent-focused UX, so adding You.com is low-risk and useful for users who want another web/news option with LLM-friendly snippets.\n\n## Why this repo\n- Small, active AI-agent search toolkit (<50 stars)\n- Clear provider interface ( trait) and mode routing\n- Existing multi-provider architecture where You.com fits naturally\n\n## What changed\n- Added a new provider module: \n - Uses You.com Search API ()\n - Supports general search and news search\n - Handles freshness mapping ( → )\n - Applies include/exclude domain filters via query operators\n - Includes auth, API status, and rate-limit error handling\n- Wired provider into runtime:\n - (module + provider registry)\n - (include in general/news/deep mode routing)\n - provider validation + JSON schema values + config show list\n- Added config support:\n - adds + / checks\n - includes \n- Updated docs + examples:\n - README provider count (11 → 12)\n - Providers table entry for You.com\n - env var setup ()\n - usage example with \n- Updated integration tests for provider/docs expectations\n\n## Setup\nYou can configure You.com via either: \n- config file: \n- env var: (or )\n\nUsage example:\n\n\n## Validation\n- Local branch builds logically against existing provider patterns and type signatures.\n- I could not run Rust checks in this environment because is not installed ().\n- Existing CI should validate compile/tests; happy to adjust quickly if anything fails.\n\n## Backward compatibility / risk\n- Fully additive change: no existing provider behavior removed\n- Existing config keys and commands remain unchanged\n- is optional and only active when key is configured\n\nIf you’d prefer different routing defaults (e.g., only in ), I can revise quickly. Happy to adapt naming, env var conventions, or response shaping to your preferences.