Improve app UX (server setup, status, gallery, log) and allow

manual CI publishes

- Settings: prefill an editable example server URL, add a "Test
  connection" button
- Front page now shows the receipts list (Overview) with a column
  header and an empty-state message
- Add a connection status bar (polls /health) shown on every screen
- Capture: add "Choose from gallery" alongside the camera
- Add an in-app "App log" screen; ApiClient/CaptureViewModel/
  OverviewViewModel/ConnectionStatusViewModel now log key events,
  including the actual connection-failure reason (not just pass/fail)
- .gitea/workflows/build.yml: publish to dl.ladkau.de on a manual
  "Run workflow" dispatch too, not just push
- README.md: document the CI secrets (REGISTRY_USER/PASSWORD,
  DL_SFTP_KEY) that must be configured in Gitea, separate from the
  local registry.env

README.md

@@ -102,6 +102,19 @@ registry, published via `./upload-image.sh` after `./build-image.sh`)
 and publishes the APK to dl.ladkau.de on every push to the default
 branch.
 
+CI needs its own copy of credentials, separate from your local
+`registry.env` (which only `build-image.sh`/`upload-image.sh`/
+`run-image.sh` on your machine read - Gitea Actions never sees it). Add
+these as **repo Settings → Actions → Secrets**:
+
+- `REGISTRY_USER` / `REGISTRY_PASSWORD` - to pull the private
+  `build-image/` image (same values as `registry.env`)
+- `DL_SFTP_KEY` - the private key for the SFTP publish step to
+  dl.ladkau.de
+
+Without them, the workflow fails early (pulling the build image, or
+publishing) rather than partway through the build.
+
 ## Running
 
 **Inspect the pipeline stage by stage**, for development/debugging one