Add dialogue portrait side placement

tools/validate_data.ps1

@@ -101,6 +101,7 @@ $validSkillKinds = @("damage", "heal", "support")
 $validSkillTargets = @("enemy", "ally", "self", "any")
 $validSkillStats = @("atk", "def", "int", "agi")
 $validSkillEffectTypes = @("stat_bonus")
+$validDialogueSides = @("left", "right")
 $validPortraitPathPattern = '^res://.+\.(png|jpg|jpeg|webp)$'
 $knownFlagIds = New-Object System.Collections.Generic.HashSet[string]
 $knownFlagValueKinds = @{}
@@ -1207,6 +1208,12 @@ function Check-Dialogue-Line($Line, [string]$Context) {
     if (Has-Prop $Line "portrait") {
         Check-Portrait-Path (Get-Prop $Line "portrait" "") "$Context portrait"
     }
+    if (Has-Prop $Line "side") {
+        $side = ([string](Get-Prop $Line "side" "")).Trim().ToLowerInvariant()
+        if (-not $validDialogueSides.Contains($side)) {
+            Fail "$Context has unknown dialogue side: $side"
+        }
+    }
 }
 
 function Check-Portrait-Path($Portrait, [string]$Context) {