fix(payment): bound newest-first mempool scans

[Alike001]

Summary

• filter invoice-relevant mempool entries before decoding
• sort candidates newest-first so newly broadcast customer payments are checked first
• cap each poll at 12 getrawtransaction calls instead of scanning the whole Testnet mempool
• keep truncated post-expiry scans fail-closed
• retain mined-block confirmation as the final payment authority

Why

A production poll attempted more than 100 getrawtransaction requests. Roughly 20 succeeded and the rest were rejected, filling the checkout evidence panel with red calls and unnecessarily stressing the free QuickNode endpoint.

Verification

• formatting, lint, and type-check passed
• payment verifier: 23 passed
• remaining suite: 129 passed, 1 skipped; two PGlite startup timeouts passed on clean isolated reruns (14 + 3 tests)
• secret scan passed
• production build passed

Closes #37

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Project	Deployment	Actions	Updated (UTC)
zecceipt	Ready	Preview	Aug 30, 2026 3:07pm

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