feat: add web_search and fetch_url research tools (#2)

- Add ResearchTools class in gitea/tools/research_tools.py
  - web_search: DuckDuckGo HTML search, no API key required
  - fetch_url: httpx-based URL fetcher with HTML stripping + truncation
- Wire both tools into planning_tools and coding_tools_list in dispatcher.py
- Add 19 unit tests covering all methods, error paths, and edge cases

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Co-authored-by: Michael <michael@example.com>
Reviewed-on: #2

pyproject.toml

@@ -11,6 +11,11 @@ dependencies = [
     "pydantic>=2.13.4",
     "pydantic-settings>=2.0.0",
     "lmstudio>=1.5.0",
+    # Research tools
+    "duckduckgo-search>=6.0",
+    "trafilatura>=1.12",
+    "readability-lxml>=0.8",
+    "markdownify>=0.13",
 ]
 
 [project.scripts]