fix(ux): add helpful empty state messages to list views (#164)

[lmduy2612]

Closes #164.

Summary of Changes

• Creates reusable, accessible component with status role, custom icon, descriptive guidance, and optional CTA action.
• Integrates empty state and explicit loading separation in and .
• Ensures empty state is never displayed prematurely during active network loading cycles.
• Full Vitest unit test suite covering empty state styling, messaging, and layout.