OneDeploy 503 Service Unavailable on Linux Python App Service for >24h, post-auth, multiple unrelated commits

## Summary

GitHub Actions deploys via `azure/webapps-deploy@v3` to a Linux Python 3.11 App Service have been failing with HTTP 503 from OneDeploy for over 24 hours, across multiple unrelated commits. SCM auth layer responds normally; the 503 happens post-authentication, deeper in the OneDeploy/Kudu pipeline.

## Environment

- App Service name: `wapd-image-finder`
- Runtime: Linux Python 3.11
- Deploy method: GitHub Actions OIDC -> `azure/webapps-deploy@v3` -> OneDeploy (zip)
- Region: East US
- Date range observed: 2026-05-08 through 2026-05-09 UTC

## Symptoms

- Build step succeeds.
- Deploy step calls OneDeploy with a valid OAuth token.
- Response: `HTTP 503 Service Unavailable`.
- Failure log:
```
Failed to deploy web package using OneDeploy to App Service.
Service Unavailable (CODE: 503)
```
- Initial failures (2026-05-09 ~04:45 UTC): fast 503 returned in ~1m36s.
- Latest failure (2026-05-09 ~20:43 UTC): ~6 min stall between "Deployment Step Started" and "Package deployment using OneDeploy initiated", then 503.

## Diagnostic data ruling out customer-side cause

- `curl -I https://wapd-image-finder.scm.azurewebsites.net/` -> 401 (auth challenge, expected, fast).
- `curl -I https://wapd-image-finder.scm.azurewebsites.net/api/publish` -> 401 (reachable).
- `curl -I https://wapd-image-finder.scm.azurewebsites.net/api/zipdeploy` -> 401 (reachable).
- Same workflow + OIDC config has succeeded multiple times prior to 2026-05-08.
- Three different commits failing the same way, none of which touch infrastructure or deploy config.

## Ask

- Is OneDeploy currently degraded for Linux Python in East US?
- Is there a documented alternate deploy path recommended while OneDeploy is recovering (e.g., `az webapp deploy --type zip` direct, Kudu zipdeploy via REST)?
- Acknowledgment so we can correlate against any in-flight Microsoft incident ticket.

Filing this as an audit-trail issue. Will update with resolution once OneDeploy clears.