chore(config,docs): remove MaterialsFile setting and update deployment notes

- Drop PepSettings:MaterialsFile from appsettings.json
- Update DEPLOY.md with guidance on service account and note that materials are sourced from DB
- Remove obsolete reference to material.lfn

scripts/DEPLOY.md

@@ -23,6 +23,8 @@ This will:
 - Open Windows Firewall for port 8085
 - Start the service automatically
 
+By default, the service runs under the current user (you will be prompted for your password). To install as LocalSystem instead, add `-UseLocalSystem`.
+
 ### Custom Deployment
 
 ```powershell
@@ -34,6 +36,35 @@ powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 `
   -OpenFirewall
 ```
 
+### Run Service As User (for network access)
+
+By default the service runs under your current user to allow access to network shares. You can also explicitly choose an account:
+
+```powershell
+# Prompt for the current user's password and install the service to run as you
+powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 -RunAsCurrentUser
+
+# Or specify explicit credentials (you will get a secure credential prompt)
+$cred = Get-Credential  # Enter DOMAIN\User or .\LocalUser
+powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 -ServiceCredential $cred
+
+# Or pass a domain user and get prompted for its password
+powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 -DomainUser "MYDOMAIN\\jdoe"
+
+# Or pass domain and user separately
+powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 -Domain "MYDOMAIN" -User "jdoe"
+
+### Install As LocalSystem (opt-out of default user)
+
+```powershell
+powershell -ExecutionPolicy Bypass -File scripts/Deploy-PepApi.ps1 -UseLocalSystem
+```
+```
+
+Notes:
+- The account must have the "Log on as a service" right. Windows typically grants this during service creation.
+- Ensure the account has read access to configured network paths in `appsettings.json`.
+
 ### Configuration
 
 After deployment, **you must update** `C:\Services\PepApi\appsettings.json`:
@@ -45,7 +76,7 @@ After deployment, **you must update** `C:\Services\PepApi\appsettings.json`:
   },
   "PepSettings": {
     "NestDirectory": "\\\\YOUR_SERVER\\PEP Nest",
-    "MaterialsFile": "C:\\Pep\\PEP2012\\CONFIG\\material.lfn"
+    "Materials": "Now sourced from database (no file path)"
   }
 }
 ```
@@ -197,7 +228,6 @@ New-NetFirewallRule -DisplayName "PepApi HTTP 8085" `
 
 - Verify service account has read access to:
   - Nest directory (`\\REMCOSRV0\PEP Nest`)
-  - Materials file (`C:\Pep\PEP2012\CONFIG\material.lfn`)
 - Configure service to run as appropriate account
 
 ### Port Already in Use