feat: add searxng search tool support, support unified results format, add readme

[feiosme]

• Implement standardized search result schema (type/title/url/content) matching Tavily's output
• Add multilingual documentation (en/zh/ru/pt/ja/es/de) for global developer accessibility

Result Format Standardization

• Adopted Tavily-compatible JSON schema:

  {
    "type": "page",
    "title": "OpenAI GPT-4",
    "url": "https://openai.com",
    "content": "Latest AI model from OpenAI..."
  }

• Added schema validation in CI pipeline

Compatibility Matrix

Feature	SearxNG	Tavily
Schema Format	✅	✅
Async Search	✅	❌
Multi-language	✅	✅
Self-hosted	✅	❌

[Copilot]

Pull Request Overview

This PR adds support for the SearXNG search tool with a unified JSON results format while updating configuration, search tool integration, and documentation in multiple languages.

• Introduces custom wrappers and result handlers for SearXNG.
• Updates the search tool selector and configuration to include SearXNG.
• Adds detailed documentation for SearXNG in various README files and updates the environment example.

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/tools/searxng_search/searxng_search_api_wrapper.py	Implements custom synchronous and asynchronous wrappers for SearXNG with unified JSON formatting.
src/tools/search.py	Integrates the new SearXNG search tool into the tool selector and adds a main test block.
src/graph/nodes.py	Applies SearXNG as an option when the selected search engine is SearXNG.
src/config/tools.py	Adds the SEARXNG entry to the search engine enum.
README_* files	Updates multilingual documentation to include setup and usage instructions for SearXNG.
.env.example	Adds an example environment variable for the SearXNG API URL.

Comments suppressed due to low confidence (1)

src/graph/nodes.py:73

• [nitpick] Using 'format' as a parameter name can be confusing as it shadows a built-in function. Consider renaming it to something clearer like 'output_format'.

            format=json,

[Copilot]

The variable 'results' is used in the print statement before it is assigned. Reorder the statements to assign 'results' before printing.

Suggested change

	print(json.dumps(results, indent=2, ensure_ascii=False))
	results = LoggedDuckDuckGoSearch(
	name="web_search", max_results=3, output_format="list"
	)
	results = LoggedDuckDuckGoSearch(
	name="web_search", max_results=3, output_format="list"
	)
	print(json.dumps(results, indent=2, ensure_ascii=False))

[mratsim]

#253 has been merged so it's likely that this PR is redundant.