Upgrade Ubuntu image and enhance security with updates and tests

[Baraujo25]

This pull request introduces several enhancements and improvements to the codebase, focusing on security, observability, dependency management, and overall project robustness. Key highlights include the addition of OpenTelemetry support, security hardening for file and HTTP endpoint handling, dependency updates, and new or improved tests. The following are the most important changes:

Security and Hardening:

• Added a new config/security.py module that provides helpers for HTTP endpoint allowlisting and sensitive path detection, preventing uploads of sensitive files and restricting unauthenticated HTTP requests to trusted domains.
• Improved validation for PerfectoToken initialization and file loading, with stricter error handling and clearer error messages.

Observability and Documentation:

• Added OpenTelemetry support with clear documentation in README.md, enabling trace and metric reporting for MCP tool calls by default, with options to disable or redirect telemetry.
• Bumped mcp[cli] dependency to >=1.27.0,<2.0.0 and added OpenTelemetry and other related dependencies in pyproject.toml.

Dependency and Build Updates:

• Updated Docker and build environments to use Ubuntu 26.04 instead of 25.10 for improved compatibility and security.
• Added Mend security scan configuration files (.whitesource, mend.config) and improved Mend scan workflow to trigger on successful test completion.

Testing and Quality:

• Added comprehensive tests for datetime utilities and help HTML sanitization/interpolation, improving coverage and reliability.

Project Management and Security Policy:

• Added a SECURITY.md file with clear guidelines for responsibly reporting vulnerabilities.
• Updated project URLs and support messaging to point to the correct GitHub organization.

These changes collectively improve the security posture, observability, and maintainability of the project.