feat: Add Anthropic Compatible provider support

- Added support for 'anthropic-compatible' provider nodes in backend.
- Implemented isAnthropicCompatible logic in open-sse for /messages URL construction and headers.
- Added UI for creating and managing Anthropic Compatible providers in the dashboard.
- Updated validation logic for Anthropic-compatible endpoints.
- Sanitize base URL input (strip trailing /messages) to prevent 404s and improve UX.
- Improve validation: use GET /models (2xx success), and support x-api-key / Authorization Bearer hybrid proxies.
- Enable model import via /models for Anthropic Compatible providers.
- Ensure Authorization is omitted when x-api-key is present to avoid strict proxy conflicts.
- Resolve Anthropic-compatible credentials by prefix during model resolution (e.g., acx/model).
- Update default executor to match provider header/url behavior for Anthropic-compatible providers.

src/app/api/providers/[id]/test/route.js

@@ -2,7 +2,7 @@ import { NextResponse } from "next/server";
 import { getProviderConnectionById, updateProviderConnection, isCloudEnabled } from "@/lib/localDb";
 import { getConsistentMachineId } from "@/shared/utils/machineId";
 import { syncToCloud } from "@/app/api/sync/cloud/route";
-import { isOpenAICompatibleProvider } from "@/shared/constants/providers";
+import { isOpenAICompatibleProvider, isAnthropicCompatibleProvider } from "@/shared/constants/providers";
 import {
   GEMINI_CONFIG,
   ANTIGRAVITY_CONFIG,
@@ -322,6 +322,32 @@ async function testApiKeyConnection(connection) {
     }
   }
 
+  // Anthropic Compatible providers - test via /models endpoint
+  if (isAnthropicCompatibleProvider(connection.provider)) {
+    let modelsBase = connection.providerSpecificData?.baseUrl;
+    if (!modelsBase) {
+      return { valid: false, error: "Missing base URL" };
+    }
+    try {
+      modelsBase = modelsBase.replace(/\/$/, "");
+      if (modelsBase.endsWith("/messages")) {
+        modelsBase = modelsBase.slice(0, -9);
+      }
+      
+      const modelsUrl = `${modelsBase}/models`;
+      const res = await fetch(modelsUrl, {
+        headers: { 
+          "x-api-key": connection.apiKey,
+          "anthropic-version": "2023-06-01",
+          "Authorization": `Bearer ${connection.apiKey}`
+        },
+      });
+      return { valid: res.ok, error: res.ok ? null : "Invalid API key or base URL" };
+    } catch (err) {
+      return { valid: false, error: err.message };
+    }
+  }
+
   try {
     switch (connection.provider) {
       case "openai": {