fix(payment): retry transient payment-history fetch errors (#162)

[TortoiseWolfe]

Summary

Fixes #162 — payment-isolation.spec.ts:113 red on all 3 browsers on main.

Root cause (reproduced): under concurrent CI backend load, getPaymentHistory()'s first attempt hits a transient Realtime/RLS 401/406 during session hydration and throws. PaymentHistory then renders a third terminal state — the "Error loading payment history" alert — which is neither the empty-state heading nor a [data-payment-item], so expect(hasNoPayments || hasPayments).toBe(true) fails. Locally (uncontended backend) the test passes 9/9, confirming load-sensitivity, not broken logic. #156's session/redirect timing change made this pre-existing contention newly visible.

Fix (root cause, helps prod too):

• PaymentHistory.refetch retries a failed fetch up to 3× with linear backoff (300/600ms) before surfacing the error alert — a momentary blip no longer strands the user on an error screen.
• The E2E assertion uses expect.poll for a stable terminal state instead of asserting on the first post-loading frame, so it never races the retry window.

Verification

• pnpm run type-check clean; prettier clean
• PaymentHistory unit tests (8) green
• payment-isolation:113 locally: 6/6 with --repeat-each=5
• CI is the real judge — the failure only manifests under concurrent-backend load, which can't be fully reproduced locally. This PR's E2E run against the shared backend is the true test.

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