feat(payments): consolidate payment history, testnet validation, and payout privacy prototype

[victor-134]

Summary

• consolidate the payment history + ledger work from [Phase 5.5] Payment history and facility payout ledger APIs with on-chain proof links #90
• include the nightly/manual testnet validation workflow from [Phase 5.5] Nightly testnet payments workflow with automatic Friendbot funding #91
• include the payout privacy prototype from [Phase 5.5] ADR + prototype: payout privacy for facilities (ADR 0005 open question) #92
• keep the branch as a single reviewable payments PR

Linked issues

Fixes #90
Fixes #91
Fixes #92

Verification

docforum-core-backend@0.0.0 typecheck
tsc --noEmit

docforum-core-backend@0.0.0 test
vitest run tests/unit --run tests/integration/payment-history.test.mts tests/unit/payment-payout-privacy.test.ts

RUN v4.1.11 /workspaces/docforum-core/backend

Test Files 12 passed (12)
Tests 102 passed (102)
Start at 22:35:13
Duration 8.75s (transform 597ms, setup 0ms, import 722ms, tests 6.21s, environment 1ms)

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[afeezorobsco-cyber]

@victor-134 Thanks for the PR. It can't be merged yet. To unblock it:

CI is failing. Here's what broke:

Backend (typecheck + test + build):

src/modules/payments/services/index.ts(83,12): error TS2304: Cannot find name 'PaymentIntentStatus'.
src/modules/payments/services/index.ts(115,36): error TS2304: Cannot find name 'PaymentIntent'.

Please fix these errors and run the same steps locally before pushing (npm run typecheck && npm test && npm run build, or cargo test for contracts).

Merge conflicts: this branch conflicts with main. Please rebase onto the latest main (git fetch upstream && git rebase upstream/main), resolve the conflicts (often ROADMAP.md, ARCHITECTURE*.md or prisma/schema.prisma), and force-push.

Push to this same branch and CI will re-run. Once it's green and conflict-free, it'll be reviewed for merge.