Make insurance file type configurable per entity (pdf vs tif)

CAMBS, RMI, CONSENSIO, and INLAND always export TIFs into the daily date
folder instead of PDFs, so engine.ps1's hardcoded "*.pdf" filter silently
found nothing to upload (no error, just "No PDFs" for every practice).
Added optional entity.json field "insurance_file_type" (defaults to "pdf"
when omitted, so existing entities are unaffected); the PT STMT split logic
already worked on filename regardless of extension, so no other changes
needed.

README.md

@@ -83,6 +83,7 @@ leave its login and every other path alone.
 | Setting | What to put |
 |---------|------------|
 | `workflow` | `insurance` if no patient files, `insurance+patient` if both |
+| `insurance_file_type` | Optional, defaults to `pdf`. Set to `tif` for an entity whose imaging system exports the daily insurance/PT STMT files as TIFs instead of PDFs (e.g. CAMBS, RMI, CONSENSIO, INLAND) |
 | `ftps.host` | FTP server address |
 | `ftps.username` | FTP username (shared across all practices) |
 | `ftps.password` | FTP password |