feat: implement first consumer-proven component slice

[jaavid]

Summary

Implements the first component slice proven by AgentReady and existing Core product needs:

• Button and IconButton
• Input, native Select and FormField
• Surface and Card
• StatusBadge with backward-compatible deprecated Badge alias
• Metric
• PageHeader
• EmptyState
• semantic light/dark tokens and complete component styles
• Persian/RTL, English/LTR, dark, disabled and validation Storybook examples
• accepted-slice usage/accessibility documentation
• updated maturity matrix

Menu and overlays remain deferred because no captured consumer flow proves them yet.

Compatibility

• Existing Button variants remain supported.
• Existing Card title API remains supported and is extended.
• Badge remains exported as a deprecated compatibility alias.
• No new runtime dependency is added.

Validation target

CI must pass lint, Vitest, TypeScript build and Storybook build.

Closes #9

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