Wallet image upload fails on dev with invalid AWS access key, and the failed upload rolls back the whole profile update

**Target branch: `keycloak`** (deployed at dev-k8s `/wallet/keycloak`, used by https://wallet-dev.treetracker.org).

## Repro (2026-08-14, wallet-dev)
Open `/wallet/customize?name=`, choose a logo or hero image, save. The PATCH fails and the app shows:

> Unknown error (The AWS Access Key Id you provided does not exist in our records.)

## Two problems
1. **Infra:** the S3 client on the dev wallet-api deployment is configured with an AWS access key that does not exist (invalid, rotated, or missing credentials in the deployment env), so every `upload()` (`server/services/S3Service.js`, `server/infra/aws/s3.js`) is rejected by AWS. Image customization is completely broken on dev.
2. **API behavior:** in `WalletService.updateWallet` the S3 upload runs inside the DB transaction, before the row update. When the upload throws, the transaction rolls back and all changes in that save are lost, including `display_name`/`about` text edits submitted alongside the image. The raw AWS SDK message also leaks to the client, giving users no actionable information.

## Suggested fix
- Infra: fix or rotate the S3 credentials (and bucket config) for the dev deployment; consider a startup or health check that validates S3 access.
- API: map S3 failures to a clear error (e.g. 502/503 "image upload unavailable") instead of passing the AWS SDK message through; optionally apply text-field updates independently of image upload success.

## Acceptance criteria
- Uploading a wallet logo/hero on wallet-dev succeeds and the image URL is persisted.
- If S3 is down, the client receives a clear error and text-only edits in the same request are not silently lost (or the behavior is documented).

Start with WalletService.updateWallet and trace the upload through server/services/S3Service.js and server/infra/aws/s3.js, then inspect the dev-k8s wallet-api deployment credentials and bucket configuration. Reproduce the failure on wallet-dev and verify that successful image uploads persist their URL, while S3 failures return a clear client error without silently losing accompanying text edits.

Written by the indexing model from the issue text.