Context

Issue #775 specifies "ProgressGauge -- circular or linear gauge for budget/utilization". PR #833 implemented a semi-circular (half-arc) gauge with sm and md size variants, but no linear variant.

Scope

Add a variant prop to ProgressGauge:

• variant: 'circular' | 'linear' (default: 'circular')
• Linear variant: horizontal bar gauge with the same color thresholds, percentage display, and accessibility attributes
• Both variants should share the same getHealthColor color logic

Acceptance criteria

• ProgressGauge accepts variant prop
• Linear variant renders a horizontal bar with percentage label
• Linear variant has proper role="meter" and aria attributes
• Storybook stories for both variants
• Unit tests for linear variant (clamping, colors, accessibility)