feat: Optimise bundle size for the Monaco text pane before release

[lornakelly]

Description

Reduce the bundle-size impact of the Monaco-based text pane before we publish the updated package. Monaco is heavy (~4 MB / ~1 MB gzip if imported wholesale - the concern flagged in the #208 editor evaluation), and the editor ships as an npm package embedded in host apps. Bring Monaco's footprint down s much as possible

Motivation

A wholesale Monaco import balloons the bundle and hurts load time for every consumer.

Proposed Implementation

No response

Definition of Done

• Implementation: Fully implemented according to the Open Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.