feat(backend): wire top-up stream endpoint to Soroban contract (#415)

[cybermax4200]

Closes #415

Changes

backend/src/services/sorobanService.ts

• Add topUpStream(streamId, amount, callerAddress) — builds, simulates,
  signs with KEEPER_SECRET_KEY, submits top_up_stream contract call,
  returns txHash

backend/src/controllers/stream.controller.ts

• Add topUpStreamHandler
  • Zod validates amount as positive integer string (XLM stroops) → 400 on failure
  • Requires authenticated user (authMiddleware) → 401 if missing
  • Enforces sender-only guard → 403 for non-sender
  • Calls topUpStream(); updates depositedAmount + lastUpdateTime in DB on success

backend/src/routes/v1/stream.routes.ts

• Register POST /:streamId/top-up behind authMiddleware
• OpenAPI JSDoc annotation included

backend/tests/integration/top-up.test.ts

• 6 tests: 200 happy path, 400 missing amount, 400 float/invalid amount,
  404 stream not found, 403 wrong caller, DB update assertion

Env var required

KEEPER_SECRET_KEY — Stellar secret key used to sign the contract transaction

[ogazboiz]

hey, main was failing CI from broken auth imports + frontend parse errors. fixed and pushed to main now. please rebase to pick up the fixes:

git fetch upstream
git rebase upstream/main
git push --force-with-lease

if there's a conflict, resolve it locally and we'll review once CI is green.

[cybermax4200]

hey, main was failing CI from broken auth imports + frontend parse errors. fixed and pushed to main now. please rebase to pick up the fixes:

git fetch upstream
git rebase upstream/main
git push --force-with-lease

if there's a conflict, resolve it locally and we'll review once CI is green.

The CI is now green

[ogazboiz]

hey, since main now has #444 merged (the cancel stream endpoint), your branch is showing stale modifications to backend/src/controllers/stream/cancel.ts and backend/src/services/sorobanService.ts that overlap with main's current state.

please rebase again to drop those:

git fetch upstream
git rebase upstream/main
# during rebase, when conflicts appear in cancel.ts or sorobanService.ts:
git checkout upstream/main -- backend/src/controllers/stream/cancel.ts backend/src/services/sorobanService.ts
git add backend/src/controllers/stream/cancel.ts backend/src/services/sorobanService.ts
git rebase --continue
git push --force-with-lease

after that, your diff should only show the actual feature for this PR and we can merge.

[cybermax4200]

hey, since main now has #444 merged (the cancel stream endpoint), your branch is showing stale modifications to backend/src/controllers/stream/cancel.ts and backend/src/services/sorobanService.ts that overlap with main's current state.

please rebase again to drop those:

git fetch upstream
git rebase upstream/main
# during rebase, when conflicts appear in cancel.ts or sorobanService.ts:
git checkout upstream/main -- backend/src/controllers/stream/cancel.ts backend/src/services/sorobanService.ts
git add backend/src/controllers/stream/cancel.ts backend/src/services/sorobanService.ts
git rebase --continue
git push --force-with-lease

after that, your diff should only show the actual feature for this PR and we can merge.

I have dropped our copy of cancel.ts and sorobanService cancel logic in favour of main's version. The branch now only adds the top-up endpoint. CI is now green, please merge