feat: Implement visual styling for field states

[lornakelly]

Description

Dependencies: #295

Scope:

• Focus state: Focus-visible ring styling on all inputs
• Changed state: Accent bar + dot indicator for dirty fields (check formState.dirtyFields)
• Error state: Field-level error styling (red border, error icon)
• Hide edit icons when isReadOnly={true}
• Implement for both light and dark modes

Motivation

Visual feedback is critical for users to understand the state of their edits and navigate the form confidently. Without clear visual indicators, users cannot tell which fields they've modified, where their focus is, or which fields have errors

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.