feat: add accessible multi-step escrow funding wizard with state machine (Closes #24)

[waterWang]

Description

Implements Accessible Multi-Step Escrow Funding Flow Backed by a State Machine (Closes #24).

Features

• Finite State Machine — Uses useReducer with explicit step transitions (funding → milestones → review → wallet → success)
• 5-Step Wizard:
  1. Funding Details — Enter escrow amount (XLM), recipient Stellar public key, and optional memo
  2. Milestone Schedule — Define milestone-based payouts with percentage allocation, descriptions, and due dates
  3. Review & Confirm — Summary view of all entered data before final submission
  4. Connect Wallet — Simulated wallet connection flow (ready for Freighter/Lobstr integration)
  5. Success — Transaction confirmation with summary
• Keyboard Navigation — Full Tab/Enter/Escape support, focus management on step transitions
• Screen-Reader Announcements — aria-live="polite" region announces step changes, aria-current="step" on progress indicator
• Resumable Progress — Wizard state persisted to localStorage; resumes from where user left off across page reloads
• Responsive Design — Mobile-first layout with Tailwind CSS v4, step labels hidden on mobile, visible on tablet+
• Validation — Form validation with error messages on each step, milestone percentage must total 100%
• TypeScript — Full type safety with discriminated union types for actions and state

Technical Details

• Route: /fund-escrow
• New files: 8 component files + 1 hook file
• Zero new dependencies — Uses only existing project dependencies (React, Next.js, Tailwind CSS)
• Architecture: useEscrowWizard hook handles all state machine logic, components are pure presentational

Tests

• npm run typecheck — passes (pre-existing .next/types/validator.ts error only)
• npm run lint — 0 errors
• npm run build — passes, /fund-escrow route generated

[vercel]

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