Add dialogue portrait slots

tools/validate_data.ps1

@@ -1203,6 +1203,19 @@ function Check-Dialogue-Line($Line, [string]$Context) {
     if ([string]::IsNullOrWhiteSpace([string](Get-Prop $Line "text" ""))) {
         Fail "$Context has an empty dialogue text."
     }
+    if (Has-Prop $Line "portrait") {
+        $portrait = Get-Prop $Line "portrait" ""
+        if ($portrait -is [System.Array] -or $portrait -is [System.Management.Automation.PSCustomObject]) {
+            Fail "$Context portrait must be a string resource path."
+        }
+        if ([string]::IsNullOrWhiteSpace([string]$portrait)) {
+            Fail "$Context has an empty portrait path."
+        }
+        $portraitText = [string]$portrait
+        if ($portraitText -notmatch '^res://.+\.(png|jpg|jpeg|webp)$') {
+            Fail "$Context portrait must be a res:// image path."
+        }
+    }
 }
 
 function Check-Post-Battle-Dialogue($Dialogue, [string]$ScenarioId) {