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>

app/api/chat/route.ts

@@ -8,7 +8,7 @@ import {
     streamText,
 } from "ai"
 import { z } from "zod"
-import { getAIModel } from "@/lib/ai-providers"
+import { getAIModel, supportsPromptCaching } from "@/lib/ai-providers"
 import { findCachedResponse } from "@/lib/cached-responses"
 import {
     getTelemetryConfig,
@@ -202,6 +202,12 @@ async function handleChatRequest(req: Request): Promise<Response> {
     // Get AI model from environment configuration
     const { model, providerOptions, headers, modelId } = getAIModel()
 
+    // Check if model supports prompt caching
+    const shouldCache = supportsPromptCaching(modelId)
+    console.log(
+        `[Prompt Caching] ${shouldCache ? "ENABLED" : "DISABLED"} for model: ${modelId}`,
+    )
+
     // Get the appropriate system prompt based on model (extended for Opus/Haiku 4.5)
     const systemMessage = getSystemPrompt(modelId)
 
@@ -262,7 +268,7 @@ ${lastMessageText}
     // Add cache point to the last assistant message in conversation history
     // This caches the entire conversation prefix for subsequent requests
     // Strategy: system (cached) + history with last assistant (cached) + new user message
-    if (enhancedMessages.length >= 2) {
+    if (shouldCache && enhancedMessages.length >= 2) {
         // Find the last assistant message (should be second-to-last, before current user message)
         for (let i = enhancedMessages.length - 2; i >= 0; i--) {
             if (enhancedMessages[i].role === "assistant") {
@@ -287,17 +293,21 @@ ${lastMessageText}
         {
             role: "system" as const,
             content: systemMessage,
-            providerOptions: {
-                bedrock: { cachePoint: { type: "default" } },
-            },
+            ...(shouldCache && {
+                providerOptions: {
+                    bedrock: { cachePoint: { type: "default" } },
+                },
+            }),
         },
         // Cache breakpoint 2: Current diagram XML context
         {
             role: "system" as const,
             content: `Current diagram XML:\n"""xml\n${xml || ""}\n"""\nWhen using edit_diagram, COPY search patterns exactly from this XML - attribute order matters!`,
-            providerOptions: {
-                bedrock: { cachePoint: { type: "default" } },
-            },
+            ...(shouldCache && {
+                providerOptions: {
+                    bedrock: { cachePoint: { type: "default" } },
+                },
+            }),
         },
     ]