fix: add trash/delete collective tools and address review feedback (round 4)

Add collectives_trash_collective and collectives_delete_collective MCP
tools with proper destructiveHint annotations. Refactor integration test
fixture to use MCP tools for cleanup instead of direct httpx/OCS calls.
Optimize _get_ocs_headers() to class-level constant.

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

pyproject.toml

@@ -135,6 +135,7 @@ dev = [
     "ruff>=0.11.13",
     "reportlab>=4.0.0",
     "ty>=0.0.1a25",
+    "pytest-otel>=2.0.1",
 ]
 
 [project.scripts]