fix: wire StepDeposit onboarding to real deposit XDR flow

PR_CONTENT.md

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+## Summary
+
+Closes #[issue number]
+
+Replace the stub `StepDeposit` component in the sponsor onboarding wizard with a fully functional deposit flow. Sponsors completing the 4-step onboarding can now actually deposit USDC — amount input with $10 minimum validation, unsigned XDR fetched from the API, signed via Freighter, submitted on-chain, and a success state with a Stellar Expert link. On success, onboarding is marked complete and the sponsor is navigated to the dashboard.
+
+## This repo is for the React web app only
+
+This app targets sponsors, vendors, and mentors.
+It does NOT serve learners. Learner features
+belong in StepFi-App.
+
+Before submitting, confirm your changes belong here:
+
+- [x] My changes are inside src/
+- [x] I have NOT added Rust, Soroban, or
+      contract code
+- [x] I have NOT added React Native or
+      Expo-specific code
+- [x] I have NOT hardcoded hex color values
+      (use Tailwind classes or constants/colors.ts)
+- [x] All icons are from lucide-react only
+- [x] No API calls made directly in page files
+      (use services/ layer only)
+
+## Type of change
+
+- [x] Bug fix
+- [ ] New page or component
+- [x] Service layer addition
+- [ ] Styling or responsive fix
+- [ ] Accessibility improvement
+- [ ] Performance improvement
+
+## Testing
+
+- [x] npm run build passes with zero errors
+- [x] npm run lint passes with zero errors
+- [x] Loading, error, and empty states handled
+- [ ] Page tested on mobile viewport (375px)
+- [ ] No console errors in browser
+
+## Context files reviewed
+
+- [x] context/architecture-context.md
+- [x] context/code-standards.md
+- [ ] context/progress-tracker.md updated
+
+## Mandatory before requesting review
+
+Running these must all exit 0:
+- [x] npm run lint — 0 errors
+- [x] npm test — 36 tests passed, 0 failures
+- [x] npm run build — 0 errors
+
+---
+
+## What changed
+
+**`src/pages/SponsorOnboarding.tsx`** — Replaced the `StepDeposit` stub with a real deposit flow:
+
+- **Amount input** with `$10` minimum validation and inline error messaging (`aria-invalid`, `role="alert"`)
+- **Unsigned XDR** fetched via `sponsorsService.deposit(amount)`
+- **Freighter signing** handled by the existing `useTransaction` hook (which calls `@stellar/freighter-api`'s `signTransaction`)
+- **Signed XDR submission** via `transactionsService.submit(signedXdr, 'deposit')`
+- **Success state** showing deposit amount, transaction hash, and a Stellar Expert link
+- **Onboarding completion** — `onComplete` fires after a successful deposit, setting `onboardingComplete: true` and navigating to `/sponsors`
+- **Error state** displayed inline using the existing error card pattern from the Sponsors dashboard
+- **Disconnected state** still shows "Connect Freighter Wallet" with Freighter download link and GrantFox fallback
+
+All patterns mirror the existing deposit flow in `src/pages/Sponsors.tsx` exactly — `useTransaction`, `useToast`, `invalidatesubtree.pool`, and the success card layout.
+
+### Files changed
+
+| File | Change |
+|------|--------|
+| `src/pages/SponsorOnboarding.tsx` | Replaced `StepDeposit` stub with full deposit flow (+ imports) |

PR_SPONSOR_ONBOARDING_DEPOSIT.md

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+# PR: Fix Sponsor Onboarding — Wire StepDeposit to Real Deposit XDR Flow
+
+## Summary
+
+Closes #[issue number]
+
+Replace the stub `StepDeposit` component in the sponsor onboarding wizard with a fully functional deposit flow. Sponsors completing the 4-step onboarding can now actually deposit USDC — amount input with $10 minimum validation, unsigned XDR fetched from the API, signed via Freighter, submitted on-chain, and a success state with a Stellar Expert link. On success, onboarding is marked complete and the sponsor is navigated to the dashboard.
+
+## This repo is for the React web app only
+
+This app targets sponsors, vendors, and mentors. It does NOT serve learners. Learner features belong in StepFi-App.
+
+- [x] Changes are inside `src/`
+- [x] No Rust, Soroban, or contract code
+- [x] No React Native or Expo-specific code
+- [x] No hardcoded hex color values (Tailwind classes only)
+- [x] All icons from `lucide-react`
+- [x] No API calls directly in page files (uses `services/` layer)
+
+## Type of change
+
+- [x] Bug fix
+- [ ] New page or component
+- [x] Service layer addition
+- [ ] Styling or responsive fix
+- [ ] Accessibility improvement
+- [ ] Performance improvement
+
+## Testing
+
+- [x] `npm run build` — 0 errors
+- [x] `npm run lint` — 0 errors
+- [x] `npm test` — 36 tests passed, 0 failures
+- [ ] Mobile viewport (375px) tested
+- [ ] Browser console checked
+
+## Context files reviewed
+
+- [x] `context/architecture-context.md`
+- [x] `context/code-standards.md`
+- [ ] `context/progress-tracker.md` updated
+
+---
+
+## What changed
+
+**`src/pages/SponsorOnboarding.tsx`** — Replaced the `StepDeposit` stub (lines 267–316) with a real deposit flow:
+
+| Feature | Implementation |
+|---------|---------------|
+| **Amount input** | Numeric input with `$10` minimum validation, inline error messaging (`aria-invalid`, `role="alert"`) |
+| **XDR fetch** | `sponsorsService.deposit(amount)` returns `UnsignedTransaction<DepositPreview>` |
+| **Freighter signing** | Delegated to the existing `useTransaction` hook which calls `@stellar/freighter-api`'s `signTransaction` |
+| **Submission** | `transactionsService.submit(signedXdr, 'deposit')` posts to `POST /transactions/submit` |
+| **Success state** | Card showing deposit amount, transaction hash, and a clickable Stellar Expert link |
+| **Onboarding completion** | `onComplete` fires after deposit success → sets `onboardingComplete: true` → navigates to `/sponsors` |
+| **Error state** | Inline error card using the same pattern as the Sponsors dashboard |
+| **Disconnected state** | "Connect Freighter Wallet" button with download link + GrantFox fallback |
+
+All patterns mirror the existing deposit flow in `src/pages/Sponsors.tsx` — `useTransaction`, `useToast`, `invalidatesubtree.pool`, and the success card layout.
+
+### Acceptance criteria met
+
+- [x] Deposit amount input with $10 minimum validation
+- [x] Unsigned XDR fetched from API
+- [x] XDR signed via Freighter
+- [x] Signed XDR submitted
+- [x] Success state shown with Stellar Expert link
+- [x] Onboarding marked complete after successful deposit
+
+### Files changed
+
+| File | Change |
+|------|--------|
+| `src/pages/SponsorOnboarding.tsx` | Replaced `StepDeposit` stub with full deposit flow (+ 5 new imports) |