Web Search provider defaults are split by capability

What changed

Web Search now has separate default provider settings for keyword search and URL content fetching. Jina is shown as one provider, Jina, with both capabilities instead of a separate Jina Reader entry. A new built-in Fetch provider is available for URL content fetching.

Why this matters to the user

Users configuring Web Search will see two default-provider selectors in Settings: one for normal search and one for fetching URLs. Existing v2 development data that referenced the removed jina-reader provider id or the single Web Search default provider will not be preserved by this refactor.

What the user should do

Select defaults for both Web Search capabilities in Settings. Users who rely on Jina should configure the single Jina provider and choose it where needed.

Notes for release manager

This is a v2 development breaking change. Per the architecture decision, no compatibility migration is included for the old v2-only chat.web_search.default_provider key or jina-reader provider id. Existing v2 development provider overrides using the previous flat apiHost shape are also not preserved; users should reconfigure affected provider hosts in Settings.