feat: add extended placeholder validation

src/models/Config.tsx

@@ -109,5 +109,50 @@ export class Config {
 
     return missingParams;
   }
+
+  /**
+   * Validates that all @placeholders@ in template have corresponding params.
+   * Checks DEFAULT env first, then all custom envs.
+   * Returns array of placeholder names that are not defined.
+   */
+  validatePlaceholders(): string[] {
+    const defaultEnv = this.envs.find(e => e.name === "DEFAULT");
+    const customEnvs = this.envs.filter(e => e.name !== "DEFAULT");
+    
+    // Collect all param names from DEFAULT
+    const defaultParamNames = new Set(
+      defaultEnv?.params.map(p => p.name).filter(n => n && n.trim() !== "") || []
+    );
+    
+    // Collect all param names from all custom envs
+    const customParamNames = new Set(
+      customEnvs.flatMap(e => e.params.map(p => p.name).filter(n => n && n.trim() !== ""))
+    );
+    
+    // Extract all @placeholders@ from template
+    const placeholderRegex = /@(\w+)@/g;
+    const placeholdersInTemplate = new Set<string>();
+    let match;
+    while ((match = placeholderRegex.exec(this.template.content)) !== null) {
+      placeholdersInTemplate.add(match[1]);
+    }
+    
+    // Find placeholders that don't have matching params
+    const missingParams: string[] = [];
+    for (const placeholder of placeholdersInTemplate) {
+      if (placeholder === Config.ENV_NAME_PARAM) continue; // Skip built-in
+      
+      // Check if exists in DEFAULT or in ANY custom env
+      const inDefault = defaultParamNames.has(placeholder);
+      const inCustom = customParamNames.has(placeholder);
+      
+      // Valid if: in DEFAULT, or in at least one custom env
+      if (!inDefault && !inCustom) {
+        missingParams.push(placeholder);
+      }
+    }
+    
+    return missingParams;
+  }
 }