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/tests/test_doctor.py

@@ -198,6 +198,38 @@ class TestCheckWebSearch:
         assert result.fix is not None
         assert "make setup" in result.fix
 
+    def test_brave_with_key_ok(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("BRAVE_SEARCH_API_KEY", "bsa-test")
+        cfg = tmp_path / "config.yaml"
+        cfg.write_text("config_version: 5\ntools:\n  - name: web_search\n    use: deerflow.community.brave.tools:web_search_tool\n")
+        result = doctor.check_web_search(cfg)
+        assert result.status == "ok"
+
+    def test_brave_without_key_warns(self, tmp_path, monkeypatch):
+        monkeypatch.delenv("BRAVE_SEARCH_API_KEY", raising=False)
+        cfg = tmp_path / "config.yaml"
+        cfg.write_text("config_version: 5\ntools:\n  - name: web_search\n    use: deerflow.community.brave.tools:web_search_tool\n")
+        result = doctor.check_web_search(cfg)
+        assert result.status == "warn"
+        assert result.fix is not None
+        assert "BRAVE_SEARCH_API_KEY" in result.fix
+
+    def test_brave_with_inline_api_key_ok(self, tmp_path, monkeypatch):
+        monkeypatch.delenv("BRAVE_SEARCH_API_KEY", raising=False)
+        cfg = tmp_path / "config.yaml"
+        cfg.write_text('config_version: 5\ntools:\n  - name: web_search\n    use: deerflow.community.brave.tools:web_search_tool\n    api_key: "inline-key"\n')
+        result = doctor.check_web_search(cfg)
+        assert result.status == "ok"
+        assert "api_key configured" in result.detail
+
+    def test_brave_with_api_key_env_ref_ok(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("BRAVE_SEARCH_API_KEY", "bsa-test")
+        cfg = tmp_path / "config.yaml"
+        cfg.write_text("config_version: 5\ntools:\n  - name: web_search\n    use: deerflow.community.brave.tools:web_search_tool\n    api_key: $BRAVE_SEARCH_API_KEY\n")
+        result = doctor.check_web_search(cfg)
+        assert result.status == "ok"
+        assert "api_key" in result.detail
+
     def test_no_search_tool_warns(self, tmp_path):
         cfg = tmp_path / "config.yaml"
         cfg.write_text("config_version: 5\ntools: []\n")