feat: deadline banners (#734), analytics (#718), tx metrics (#720), dual-auth ADR (#713)

[Salmatcre8]

Summary

Four monitoring / UX / docs items, all in this repo:

Closes #734
Closes #718
Closes #720
Closes #713

#734 — Landlord deadline reminder banner

• New: components/dashboard/DeadlineBanners.tsx — on dashboard load, shows a dismissible amber banner for each active escrow whose deadline is within 72 hours. Dismissals persist in localStorage.
• New: components/dashboard/deadline-utils.ts — JSX-free selection/format helpers (so the logic is unit-testable under node --test).
• Modified: app/dashboard/page.tsx — renders <DeadlineBanners escrows={escrows} /> above the portfolio summary.
• Acceptance: a deadline 48h away produces a warning banner (covered by a test).

#718 — Privacy-first page analytics

• New: components/ui/analytics.tsx — loads Plausible (cookieless, GDPR-compliant) via next/script, only when NEXT_PUBLIC_PLAUSIBLE_DOMAIN is set and Do Not Track / GPC is off. Exposes trackEvent() for the key events (escrow-creation start, wallet connect, contribution complete); Plausible auto-records page views.
• Modified: app/layout.tsx — mounts <Analytics />.
• No new dependency (script-tag integration). Respects DNT by default.

#720 — Transaction failure-rate metrics

• New: lib/metrics.ts — in-process counters with recordTransaction() + getMetrics() returning { total_transactions, failed_transactions, failure_rate_percent } (plus a per-type breakdown).
• New: app/api/metrics/route.ts — GET /api/metrics.
• Modified: lib/stellar/actions/contribute.ts — wraps submit/confirm to record success/failure.

#713 — ADR for the dual authentication system

• New: docs/adr/002-dual-auth.md — documents why email-JWT and Stellar-wallet auth must coexist (account identity vs. on-chain financial identity, custody boundary, onboarding), plus a migration path if either is removed. Follows the format of the existing 001-file-storage.md.

Verified terminal output

$ node --test ... lib/metrics.test.ts components/dashboard/deadline-utils.test.ts
ℹ tests 12
ℹ pass 12
ℹ fail 0

tsc --noEmit: no new errors in changed files (repo has 21 pre-existing baseline errors unrelated to this PR).

Acceptance criteria

• [Issue #238] Landlord: Deadline Reminder Banner #734 — a deadline 48h away shows a warning banner on the dashboard
• [Issue #222] Monitoring: Privacy-First Page Analytics #718 — visiting a page generates a page-view event (Plausible, when configured; DNT respected)
• [Issue #224] Monitoring: Transaction Failure Rate Metrics #720 — GET /api/metrics returns accurate transaction failure statistics
• [Issue #217] Docs: ADR for Dual Authentication System #713 — ADR clearly explains why both auth systems must coexist

Note: #720's metrics are in-process (reset on restart, per-instance) — sufficient for current visibility; the store can be swapped for Redis/DB without changing the API. Analytics requires NEXT_PUBLIC_PLAUSIBLE_DOMAIN to be set in the deployment to emit events.

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