The three migrated providers (brave-free, ddgs, searxng) are now dispatched
through agent.web_search_registry.get_provider() instead of importing
their concrete classes directly. The four inline providers (parallel, exa,
tavily, firecrawl) keep their existing branches — they live in
tools/web_tools.py itself and aren't part of this spike's plugin extraction.
The legacy tools/web_providers/{brave_free,ddgs,searxng}.py modules are
still in place (untouched by this commit) — Task 10 deletes them once the
real migration PR is ready. Keeping them alive during the spike means
revertibility is trivial.
E2E verified:
1. Plugin discovery registers ['brave-free','ddgs','searxng']
2. Config web.search_backend: brave-free resolves to the plugin instance
3. Dispatch result matches the original {success, data.web[]} contract
4. compile OK; no new LSP errors beyond pre-existing ones in web_tools.py
6bd16a645b