feat(community): add Brave Search web search tool (#3528)

* feat(community): add Brave Search web search tool

Add a community web_search provider backed by the official Brave Search
API (https://api.search.brave.com/res/v1/web/search). API key is read
from the tool config (inline api_key) or the BRAVE_SEARCH_API_KEY env
var. Output schema (title/url/content) matches existing search tools.
No new dependencies (uses the existing httpx). Also wires up the setup
wizard, doctor health check, config example, and EN/ZH docs.

* refactor(community): drop redundant [:count] slice in Brave search

The Brave API already caps results via the `count` request param, so
client-side slicing was redundant. Tests now simulate the API honoring
`count` instead of relying on the slice. Addresses PR review nit.

* style(tests): apply ruff format to test_doctor.py

Collapse multiline write_text calls onto single lines to satisfy the
CI ruff formatter (lint-backend was failing on format --check).

backend/packages/harness/deerflow/community/brave/__init__.py

@@ -0,0 +1,3 @@
+from .tools import web_search_tool
+
+__all__ = ["web_search_tool"]