feat: implement illustrated EmptyState component across list views

[gospeltout]

Summary

Implemented a unified, illustrated EmptyState component to transform plain empty list views into visual onboarding moments with primary call-to-action buttons. Applied across Tasks, Agents, History, Payments, and Notifications.

Resolves #

Changes

• Created reusable EmptyState.tsx component with icon glowing accents, titles, descriptions, and CTA action handlers.
• Added modern glassmorphism styling in EmptyState.module.css.
• Created component unit tests in EmptyState.test.tsx.
• Integrated EmptyState into RecentTasksTable, AgentTable, TaskTimeline, TransactionTable, and NotificationCenter.
• Resolved router context compatibility and TypeScript types across updated components.

Verification & Testing

• Executed npm run build (tsc --noEmit && vite build) with 0 errors and 4,773 modules transformed.

• Executed npm test (vitest run): 34/34 test files passed, 251/251 unit tests passed.

• npm test (Backend/Frontend)

• cargo test (Smart Contracts)

• cargo fmt --check && cargo clippy (Contract Linting)

Contributor Checklist

• PR title follows Conventional Commits (feat:, fix:, docs:, etc.)
• All CI checks pass locally
• Documentation updated in docs/ or README.md if applicable
• No secrets or credentials committed

Closes #360

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