feat(ui): add subtitle prop to Scorecard

[goodbounties-nanoclaw-agent]

Description

Adds an optional subtitle prop to Scorecard (packages/ui) — a short contextual/source note rendered below the trend row when a trend is present, or directly below the value row when it is not. Layout is unchanged when subtitle is omitted.

About #223

How Has This Been Tested?

• Extended tests/design-system/smoke.spec.ts (Scorecard story test) with assertions that the subtitle text renders for both the with-trend row (unique-wallets) and without-trend row (daily-flow-rate), and regenerated the tracked baseline screenshot tests/design-system/test-results/story-scorecard-default.png.
• Ran the full tests/design-system/smoke.spec.ts suite locally (45 tests across Card, GlowCard, Drawer, TokenAmount, ClaimWidget, ThemePlayground, Stepper, Scorecard, PieDonutChart, BarChart, LineAreaChart, DataTable) — all passed, no regressions.
• Built packages/ui via pnpm build (tsup) — ESM/CJS/DTS all succeeded, confirming the prop and new sub-component type-check.
• Visually verified the regenerated screenshot: subtitle renders in the correct position for both variants (bare/card) and both trend states, with no clipping.

Checklist:

• PR title matches follow: (Feature|Bug|Chore) Task Name
• My code follows the style guidelines of this project
• I have followed all the instructions described in the initial task (check Definitions of Done)
• I have performed a self-review of my own code
• 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
• I have added reference to a related issue in the repository
• I have added a detailed description of the changes proposed in the pull request. I am as descriptive as possible, assisting reviewers as much as possible.
• I have added screenshots related to my pull request (for frontend tasks)
• I have pasted a gif showing the feature.
• @mentions of the person or team responsible for reviewing proposed changes

Plan sub-issue: #225

[Copilot]

Pull request overview

Adds an optional subtitle prop to the shared Scorecard design-system component (packages/ui) to allow a short contextual/source note that renders beneath the metric (after the trend row when present, otherwise after the value row) without affecting layout when omitted.

Changes:

• Extended ScorecardProps with subtitle?: string and added a ScorecardSubtitleText styled sub-component for consistent typography/colors.
• Updated the Scorecard Storybook story data and controls to demonstrate subtitle usage with and without a trend.
• Extended the existing Playwright smoke test to assert the subtitle renders for both a with-trend and no-trend row, and adjusted viewport height for the extra line.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/ui/src/components/Scorecard.tsx	Adds subtitle prop and renders it conditionally using a new ScorecardSubtitleText component.
examples/storybook/src/stories/design-system/Scorecard.stories.tsx	Updates mock rows and Storybook controls to demonstrate subtitle in both trend/no-trend cases.
tests/design-system/smoke.spec.ts	Adds assertions for subtitle rendering and increases viewport height to avoid clipping.

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