feat(community): add Exa search as community tool provider (#1357)

* feat(community): add Exa search as community tool provider

Add Exa (exa.ai) as a new community search provider alongside Tavily,
Firecrawl, InfoQuest, and Jina AI. Exa is an AI-native search engine
with neural, keyword, and auto search types.

New files:
- community/exa/tools.py: web_search_tool and web_fetch_tool
- tests/test_exa_tools.py: 10 unit tests with mocked Exa client

Changes:
- pyproject.toml: add exa-py dependency
- config.example.yaml: add commented-out Exa configuration examples

Usage: set `use: deerflow.community.exa.tools:web_search_tool` in
config.yaml and provide EXA_API_KEY.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(community): address PR review comments for Exa tools

- Make _get_exa_client() accept tool_name param so web_fetch reads its own config
- Remove __init__.py to match namespace package pattern of other providers
- Add duplicate tool name warning in config.example.yaml
- Add regression tests for web_fetch config resolution

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Update revision in uv.lock to 3

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/uv.lock

@@ -722,6 +722,7 @@ dependencies = [
     { name = "ddgs" },
     { name = "dotenv" },
     { name = "duckdb" },
+    { name = "exa-py" },
     { name = "firecrawl-py" },
     { name = "httpx" },
     { name = "kubernetes" },
@@ -759,6 +760,7 @@ requires-dist = [
     { name = "ddgs", specifier = ">=9.10.0" },
     { name = "dotenv", specifier = ">=0.9.9" },
     { name = "duckdb", specifier = ">=1.4.4" },
+    { name = "exa-py", specifier = ">=1.0.0" },
     { name = "firecrawl-py", specifier = ">=1.15.0" },
     { name = "httpx", specifier = ">=0.28.0" },
     { name = "kubernetes", specifier = ">=30.0.0" },
@@ -871,6 +873,24 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/c1/8b/5fe2cc11fee489817272089c4203e679c63b570a5aaeb18d852ae3cbba6a/et_xmlfile-2.0.0-py3-none-any.whl", hash = "sha256:7a91720bc756843502c3b7504c77b8fe44217c85c537d85037f0f536151b2caa", size = 18059, upload-time = "2024-10-25T17:25:39.051Z" },
 ]
 
+[[package]]
+name = "exa-py"
+version = "2.10.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "httpcore" },
+    { name = "httpx" },
+    { name = "openai" },
+    { name = "pydantic" },
+    { name = "python-dotenv" },
+    { name = "requests" },
+    { name = "typing-extensions" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/fb/bb/23c9f78edbf0e0d656839be7346a2f77b9caaae8cc3cb301012c46fd7dc5/exa_py-2.10.1.tar.gz", hash = "sha256:731958c2befc5fc82f031c93cfe7b3d55dc3b0e1bf32f83ec34d32a65ee31ba1", size = 53826, upload-time = "2026-03-25T00:50:49.286Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/fc/8d/0665263aa8d51ef8e2a3955e2b56496add4879730451961b09610bbc7036/exa_py-2.10.1-py3-none-any.whl", hash = "sha256:e2174c932764fff747e84e9e6d0637eaa4a6503556014df73a3427f42cc9d6a7", size = 72270, upload-time = "2026-03-25T00:50:47.721Z" },
+]
+
 [[package]]
 name = "fake-useragent"
 version = "2.2.0"