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).

config.example.yaml

@@ -530,6 +530,16 @@ tools:
   #   max_results: 5
   #   # api_key: $SERPER_API_KEY  # Optional if SERPER_API_KEY env var is set
 
+  # Web search tool (uses Brave Search API, requires BRAVE_SEARCH_API_KEY)
+  # Brave Search returns results from an independent index. Sign up at
+  # https://brave.com/search/api/ to get a key. Unlike the DuckDuckGo
+  # `backend: brave` option above, this calls the official Brave API directly.
+  # - name: web_search
+  #   group: web
+  #   use: deerflow.community.brave.tools:web_search_tool
+  #   max_results: 5                  # Capped at 20 by the Brave Search API
+  #   # api_key: $BRAVE_SEARCH_API_KEY  # Optional if the env var is set
+
   # Web search tool (requires Tavily API key)
   # - name: web_search
   #   group: web