feat: add end-to-end private payment test

.github/workflows/privacy-e2e.yml

@@ -0,0 +1,79 @@
+name: Testnet Privacy E2E Test (Nightly)
+
+# Runs at 04:00 UTC every day (following the 03:00 smoke test)
+# Skips on dependabot branches
+on:
+  schedule:
+    - cron: '0 4 * * *'
+  workflow_dispatch: {}
+  pull_request:
+    paths:
+      - 'scripts/privacy-e2e.mjs'
+      - 'frontend/wallet/lib/privacy/**'
+      - 'frontend/wallet/e2e/privacy.spec.ts'
+      - '.github/workflows/privacy-e2e.yml'
+
+jobs:
+  privacy-e2e:
+    name: Stellar testnet — shield, private send, unshield
+    runs-on: ubuntu-latest
+    if: ${{ !startsWith(github.head_ref, 'dependabot/') }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      # ── Install stellar-sdk dependency for the script ───────────────────────
+      - name: Install dependencies
+        run: npm install @stellar/stellar-sdk
+
+      # ── Run End-to-End Privacy Test ─────────────────────────────────────────
+      - name: Run Privacy E2E Test
+        env:
+          HORIZON_URL: https://horizon-testnet.stellar.org
+        run: node scripts/privacy-e2e.mjs
+
+      # ── Notify on failure: Open GitHub Issue ────────────────────────────────
+      - name: Open GitHub issue on failure
+        if: failure()
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = `Nightly privacy E2E test failed — ${new Date().toISOString().slice(0, 10)}`;
+            const body = [
+              '## Nightly Privacy E2E Test Failure',
+              '',
+              `**Run:** https://github.com/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`,
+              '',
+              'The testnet privacy round-trip test failed.',
+              'Pipeline: Fund 2 wallets via Friendbot → Shield XLM → Private Send → Unshield → Invariant verification.',
+              '',
+              '**Triage checklist:**',
+              '- [ ] Is Friendbot healthy? <https://friendbot.stellar.org>',
+              '- [ ] Is Horizon testnet healthy? <https://horizon-testnet.stellar.org>',
+              '- [ ] Check step failure log for the exact broken step.',
+            ].join('\n');
+
+            const today = new Date().toISOString().slice(0, 10);
+            const existing = await github.rest.issues.listForRepo({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              state: 'open',
+              labels: 'testnet-smoke-failure',
+            });
+            const alreadyOpen = existing.data.some((i) => i.title.includes(today));
+            if (alreadyOpen) {
+              console.log('Issue for today already exists — skipping.');
+              return;
+            }
+
+            await github.rest.issues.create({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              title,
+              body,
+              labels: ['testnet-smoke-failure', 'privacy', 'ci'],
+            });