Engineering Layer: survive the C:\Deploy cleanup; the employee gets the icon

Engineer builds left the employee without "Configure my Engineering
Layer". First logon ran C:\Deploy\Applications\extra_engineering\
Install-EngineeringLayer.ps1, and the script itself lived in C:\Deploy:
std/eng have no autologon, so a PC that rebooted before the employee
signed in had lost C:\Deploy to the orchestrator's DeleteDeployDir task,
and nothing installed, silently.

- engineer unattend, specialize Order 37 (free slot): run the script with
  -StageOnly, copying the payload and the script to C:\PreInstall\engineering
  while C:\Deploy exists (Path 119 chars)
- first logon Order 11: run it from C:\PreInstall\engineering, falling back
  to C:\Deploy if staging did not happen
- the script (now in the repo, playbook/engineering/; it lived only on the
  server): after the install, restore the Public desktop icon if it is
  missing and the PC is not configured yet (no C:\TMP\DUU_Complete.log), and
  register Active Setup so each later user gets the icon on their own
  desktop when the Public one is gone. v3.1 puts the icon on the Public
  desktop; clicking it (configure, from GE's V: share) deletes it for all
- playbook deploys the script to gea-engineer extra_engineering; the 650 MB
  payload stays site content (documented in SITE-CUSTOMIZATION.md)

Tested in the win11 VM with the exact unattend strings and a stand-in
installer that skips the icon: specialize staged payload and script;
C:\Deploy deleted; first logon installed from the staged copy, restored the
icon and registered Active Setup. The per-user step as a new user: icon on
their desktop when the PC is unconfigured and the Public icon is gone; none
when configured or when the Public icon is there. Lint clean. Not deployed:
unattends go out only through scripts/deploy-unattend.sh.

docs/SITE-CUSTOMIZATION.md

@@ -100,6 +100,31 @@ The repo defines seven image types (see `playbook/pxe_server_setup.yml`,
 
 Trim or extend this list and the matching `shopfloor_types` filter as needed.
 
+### Engineering Layer (gea-engineer)
+
+Handled by the repo; nothing to work out per site except the payload.
+
+- `playbook/engineering/Install-EngineeringLayer.ps1` is deployed by the
+  playbook to `gea-engineer/Deploy/Applications/extra_engineering/`.
+- `FlatUnattendW10-engineer.xml` runs it twice:
+  - specialize Order 37 (`-StageOnly`) copies the payload and the script to
+    `C:\PreInstall\engineering` while `C:\Deploy` exists;
+  - first logon Order 11 installs from that copy. The bulk-enrollment
+    `DeleteDeployDir` task removes `C:\Deploy` on the next boot, so a PC
+    that reboots before the employee signs in would otherwise install
+    nothing and show no icon.
+- After the install it makes sure the "Configure my Engineering Layer"
+  icon is on the Public desktop (until the PC is configured), and registers
+  Active Setup so a later user gets the icon if someone else already used
+  it. The employee clicks it once, on the GE network: it maps V: and runs
+  `install_local_new.cmd` from GE's share, which removes the icon.
+- Log on the PC: `C:\Logs\Engineering\install-engineering-layer.log`.
+
+The site supplies the payload beside the script, in
+`gea-engineer/Deploy/Applications/extra_engineering/`:
+`engineering_layer/Engineering_Install_v3.1.exe` and `prereqs/`
+(.NET 3.5 sxs cabs, VC++ redists), about 650 MB.
+
 ### PC types (shopfloor sub-types)
 
 `playbook/shopfloor-setup/` contains per-PC-type install logic. The current
@@ -182,7 +207,9 @@ Blob storage account.
 - `\\172.16.9.1\image-upload` as the destination
 - `C:\ProgramData\GEAerospace\MediaCreator\Cache\` as the source
 
-Update both for a different site.
+Update both for a different site (`-Server`, `-CachePath`; `-WebPort` if the
+webapp is not on 9009). The script checks every file on the server through
+the webapp before the Image Import page will accept the upload.
 
 ## Recommended forward state