fix: expire stale LNbits pending invoices

[kanishka0411]

Description

Expired pending LNbits invoices can remain in the oldest pending polling batch forever when LNbits returns 404. This marks them expired only when the local invoice is already past expiresAt and the processor returns 404.
Generic processor/network errors still keep the invoice pending, and paid invoices remain completed even if their expiry timestamp has passed.

Related Issue

Fixes #333
Related to #342

Motivation and Context

The maintenance worker polls the oldest 10 pending invoices every minute. Stale invoices that LNbits has already purged (404) were being retried forever, blocking newer paid invoices from being reconciled.

How Has This Been Tested?

Added unit tests covering all four edge cases:

• expired + 404 → expire it
• expired + non-404 error → leave pending
• non-expired + 404 → leave pending
• LNbits returns unpaid + past expiry → EXPIRED; paid + past expiry → still COMPLETED

Commands run locally:

npx mocha test/unit/app/maintenance-worker.spec.ts test/unit/payments-processors/lnbits-payment-processor.spec.ts
npm run build:check
npx biome lint src/app/maintenance-worker.ts src/payments-processors/lnbits-payment-processor.ts test/unit/app/maintenance-worker.spec.ts test/unit/payments-processors/lnbits-payment-processor.spec.ts

Result: 36 passing, build clean, lint clean.

Screenshots (if appropriate):

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9e11716

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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nostream	Patch

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[coveralls]

coverage: 75.475% (+0.5%) from 74.929% — kanishka0411:fix/expire-stale-lnbits-invoices into cameri:main