URL context toggle merged into the web search switch

What changed

The separate "URL Context" button in the chat composer is gone. Fetching URLs from the prompt (Gemini URL context / Anthropic web fetch / the client web_fetch tool) is now enabled together with web search by the single web search toggle.

Why this matters to the user

Users who previously enabled URL context without web search will find that one button missing; enabling web search now also lets supported models read URLs from the prompt. Which side executes (provider-native vs Cherry's own tools) is still chosen automatically per model/provider.

What the user should do

Use the web search toggle. Nothing else — the old per-assistant URL-context setting is dropped automatically.

Notes for release manager

Can be merged with 2026-05-08-web-search-main-side-tools.md and 2026-05-06-web-search-provider-capabilities.md into one web-tools item.