fix: resolve UI conflict with ipympl and improve state management

[mlhenderson]

• Refactor AlertManager._handleNewHeaders to use a mutex-protected loop instead of recursive setTimeout to prevent race conditions and performance lag.
• Implement 'pointer-events: none' for header messages and closed side panels to ensure mouse events pass through to interactive widgets like ipympl.
• Standardize mutex locking for all StateDB access in AlertManager to ensure data atomicity.
• Enhance UI integration tests with explicit state cleanup and reliable polling synchronization to eliminate test flakiness.
• Add a dedicated regression test (ipympl_interaction.spec.ts) to verify viewport interactivity when alerts are active.
• Update CI workflow to include ipympl/matplotlib environment for automated regression testing.
• Format CSS files and update documentation for better project standards.