[micro-fix] Prevent MCP client from initialize if MCP stdio hangs

[GastonAQS]

Description

Fix MCP stdio connect to fail fast when the session never initializes, and add a unit test covering the timeout path.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

Fixes #2806

Changes Made

• Add timeout check after connection_ready.wait() in STDIO connect
• Return a clear error when the stdio session never becomes ready
• Add unit test to validate the timeout behavior

Testing

Describe the tests you ran to verify your changes:

• Unit tests pass (cd core && pytest tests/)
• Lint passes (cd core && ruff check .)
• Manual testing performed

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

Add screenshots to demonstrate UI changes.