Rename insurance_path config key to tiff_path (insurance_path still accepted)

Renamed in engine.ps1, both EXAMPLE configs, and the README. Existing
entity.json/practice.json files using insurance_path keep working - the
engine copies it to tiff_path after the merge when tiff_path isn't set.

README.md

@@ -68,7 +68,7 @@ Common reasons to add a `practice.json`:
 - The practice's files need to go to a **different folder path** on the
   server than the standard `{practice}` pattern (e.g. the imaging vendor set
   it up with a different folder name, or a nonstandard structure) — override
-  `insurance_path`, `pdf_path`, and/or `patient_path` to whatever that
+  `tiff_path`, `pdf_path`, and/or `patient_path` to whatever that
   practice actually needs
 
 You can mix and match — e.g. override just `pdf_path` for one practice and
@@ -92,7 +92,7 @@ leave its login and every other path alone.
     "tls": true,
     "username": "shared-username",
     "password": "shared-password",
-    "insurance_path": "/{practice}/Insurance",
+    "tiff_path": "/{practice}/Insurance",
     "pdf_path": "/{practice}/PDF"
   },
 
@@ -115,7 +115,7 @@ leave its login and every other path alone.
 | `ftps.tls` | Yes | `true` for FTPS (secure), `false` for plain FTP |
 | `ftps.username` | Yes | FTP username (shared across all practices) |
 | `ftps.password` | Yes | FTP password |
-| `ftps.insurance_path` | Yes | Remote folder for insurance files — keep `{practice}` in it |
+| `ftps.tiff_path` | Yes | Remote folder for insurance files — keep `{practice}` in it. (The older name `insurance_path` still works too) |
 | `ftps.pdf_path` | Yes | Remote folder for PT STMT files — keep `{practice}` in it |
 | `sftp.host` | Only if `insurance+patient` | SFTP server address |
 | `sftp.port` | No (defaults to 22) | SFTP port, only if not 22 |
@@ -137,7 +137,7 @@ uploads and nothing archives for that practice until it's fixed.
 
 **Editing JSON — the rules that bite:**
 - Key names must match **exactly** (all lowercase, underscores): `host`, not
-  `hostname`; `username`, not `user`; `insurance_path`, not `insurancepath`
+  `hostname`; `username`, not `user`; `tiff_path`, not `tiffpath`
 - Every `"key": "value"` pair ends with a comma **except the last one in its
   block** — a missing or extra comma breaks the whole file
 - Keep values inside straight double quotes (`"`). Avoid editing in Word or
@@ -159,7 +159,7 @@ If one practice needs a different login, a different folder path, or both:
 The field names are the same ones as `entity.json`, wrapped in the same
 `ftps` / `sftp` sections. A `practice.json` can also **add** a field that
 `entity.json` doesn't have at all — e.g. if `entity.json` has no
-`insurance_path` because every practice's path is different, each practice's
+`tiff_path` because every practice's path is different, each practice's
 `practice.json` can carry its own.
 
 Example — this practice only has its own PDF folder name, nothing else differs:
@@ -188,7 +188,7 @@ Example — this practice has completely different remote folders for everything
 ```json
 {
   "ftps": {
-    "insurance_path": "/SpecialFolder/Claims",
+    "tiff_path": "/SpecialFolder/Claims",
     "pdf_path": "/SpecialFolder/Statements"
   },
   "sftp": {