test: Add scope-based authorization tests for Keycloak external IdP

This enhances the Keycloak integration test suite with comprehensive
scope-based authorization validation, matching the OIDC test structure.

Changes:
- Add 3 test users to Keycloak realm (read-only, write-only, no-custom-scopes)
- Create OAuth token fixtures with different scope combinations
- Create MCP client fixtures for each scope configuration
- Add 4 new tests validating scope-based tool filtering:
  * Read-only tokens filter out write tools
  * Write-only tokens filter out read tools
  * Full access tokens show all 90+ tools
  * No custom scopes result in zero tools

Test Results:
- All 15 Keycloak integration tests pass (11 existing + 4 new)
- Validates proper JWT scope enforcement in external IdP architecture
- Confirms security isolation when users decline custom scopes

This completes ADR-002 scope authorization testing for the Keycloak
external identity provider integration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -42,7 +42,7 @@ Changelog = "https://github.com/cbcoutinho/nextcloud-mcp-server/blob/master/CHAN
 
 [tool.pytest.ini_options]
 anyio_mode = "auto"
-addopts = "-p no:asyncio -x"  # Disable pytest-asyncio plugin, use only anyio
+addopts = "-p no:asyncio -x --headed"  # Disable pytest-asyncio plugin, use only anyio
 log_cli = 1
 log_cli_level = "ERROR"
 log_level = "ERROR"