feat: support minimax model (#185)

* feat: support minimax model with XML wrapping fix

- Add wrapWithMxFile utility to properly wrap XML for draw.io
- Fix 'Not a diagram file' error when model generates raw <root> XML
- Add supportsPromptCaching check for conditional caching
- Only enable Bedrock prompt caching for Claude models

* docs: update model mention to minimax-m2 across About pages and READMEs

- Update tooltip in chat-panel.tsx to mention minimax-m2 model change
- Update English, Chinese, and Japanese About pages with model change info
- Update English, Chinese, and Japanese READMEs with demo site model note

---------

Co-authored-by: dayuan.jiang <jiangdy@amazon.co.jp>

lib/ai-providers.ts

@@ -283,3 +283,17 @@ export function getAIModel(): ModelConfig {
 
     return { model, providerOptions, headers, modelId }
 }
+
+/**
+ * Check if a model supports prompt caching.
+ * Currently only Claude models on Bedrock support prompt caching.
+ */
+export function supportsPromptCaching(modelId: string): boolean {
+    // Bedrock prompt caching is supported for Claude models
+    return (
+        modelId.includes("claude") ||
+        modelId.includes("anthropic") ||
+        modelId.startsWith("us.anthropic") ||
+        modelId.startsWith("eu.anthropic")
+    )
+}

lib/utils.ts

@@ -106,6 +106,32 @@ export function convertToLegalXml(xmlString: string): string {
     return result
 }
 
+/**
+ * Wrap XML content with the full mxfile structure required by draw.io.
+ * Handles cases where XML is just <root>, <mxGraphModel>, or already has <mxfile>.
+ * @param xml - The XML string (may be partial or complete)
+ * @returns Full mxfile-wrapped XML string
+ */
+export function wrapWithMxFile(xml: string): string {
+    if (!xml) {
+        return `<mxfile><diagram name="Page-1" id="page-1"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/></root></mxGraphModel></diagram></mxfile>`
+    }
+
+    // Already has full structure
+    if (xml.includes("<mxfile")) {
+        return xml
+    }
+
+    // Has mxGraphModel but not mxfile
+    if (xml.includes("<mxGraphModel")) {
+        return `<mxfile><diagram name="Page-1" id="page-1">${xml}</diagram></mxfile>`
+    }
+
+    // Just <root> content - extract inner content and wrap fully
+    const rootContent = xml.replace(/<\/?root>/g, "").trim()
+    return `<mxfile><diagram name="Page-1" id="page-1"><mxGraphModel><root>${rootContent}</root></mxGraphModel></diagram></mxfile>`
+}
+
 /**
  * Replace nodes in a Draw.io XML diagram
  * @param currentXML - The original Draw.io XML string