enhance: Add safety features to HTTP validation tools response (#345)

* enhance: Add safety features to HTTP validation tools response

- Add TypeScript interface (MCPToolResponse) for type safety
- Implement 1MB response size validation and truncation
- Add warning logs for large validation responses
- Prevent memory issues with size limits (matches STDIO behavior)

This enhances PR #343's fix with defensive measures:
- Size validation prevents DoS/memory exhaustion
- Truncation ensures HTTP transport stability
- Type safety improves code maintainability

All changes are backward compatible and non-breaking.

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

* chore: Version bump to 2.20.4 with documentation

- Bump version 2.20.3 → 2.20.4
- Add comprehensive CHANGELOG.md entry for v2.20.4
- Document CI test infrastructure issues in docs/CI_TEST_INFRASTRUCTURE.md
- Explain MSW/external PR integration test failures
- Reference PR #343 and enhancement safety features

Code review: 9/10 (code-reviewer agent approved)

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.20.3",
+  "version": "2.20.4",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",