Fix compilation error by creating MCP-specific screen test infrastructure

- Created McpScreenTest and McpScreenTestRender interfaces
- Rewrote CustomScreenTestImpl to implement MCP-specific interfaces instead of extending framework's buggy ScreenTestImpl
- Added all required interface methods for complete functionality
- Resolves @Override annotation error on non-existent makeWebFacade method
- Maintains MCP functionality while providing independent screen test capabilities

+/*
+ * This software is in the public domain under CC0 1.0 Universal plus a 
+ * Grant of Patent License.
+ * 
+ * To the extent possible under law, author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to the
+ * public domain worldwide. This software is distributed without any
+ * warranty.
+ * 
+ * You should have received a copy of the CC0 Public Domain Dedication
+ * along with this software (see the LICENSE.md file). If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+package org.moqui.mcp
+
+import groovy.transform.CompileStatic
+
+/**
+ * MCP-specific ScreenTest interface for simulating screen web requests
+ * This is separate from the core Moqui ScreenTest system and tailored for MCP needs
+ */
+@CompileStatic
+interface McpScreenTest {
+    McpScreenTest rootScreen(String screenLocation)
+    McpScreenTest baseScreenPath(String screenPath)
+    McpScreenTest renderMode(String outputType)
+    McpScreenTest encoding(String characterEncoding)
+    McpScreenTest macroTemplate(String macroTemplateLocation)
+    McpScreenTest baseLinkUrl(String baseLinkUrl)
+    McpScreenTest servletContextPath(String scp)
+    McpScreenTest skipJsonSerialize(boolean skip)
+    McpScreenTest webappName(String wan)
+    
+    McpScreenTestRender render(String screenPath, Map<String, Object> parameters, String requestMethod)
+    void renderAll(List<String> screenPathList, Map<String, Object> parameters, String requestMethod)
+    
+    List<String> getNoRequiredParameterPaths(Set<String> screensToSkip)
+    
+    long getRenderCount()
+    long getErrorCount()
+    long getRenderTotalChars()
+    long getStartTime()
+}
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+/*
+ * This software is in the public domain under CC0 1.0 Universal plus a 
+ * Grant of Patent License.
+ * 
+ * To the extent possible under law, author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to the
+ * public domain worldwide. This software is distributed without any
+ * warranty.
+ * 
+ * You should have received a copy of the CC0 Public Domain Dedication
+ * along with this software (see the LICENSE.md file). If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+package org.moqui.mcp
+
+import groovy.transform.CompileStatic
+import org.moqui.screen.ScreenRender
+
+/**
+ * MCP-specific ScreenTestRender interface for screen rendering results
+ * This is separate from the core Moqui ScreenTest system and tailored for MCP needs
+ */
+@CompileStatic
+interface McpScreenTestRender {
+    ScreenRender getScreenRender()
+    String getOutput()
+    Object getJsonObject()
+    long getRenderTime()
+    Map getPostRenderContext()
+    List<String> getErrorMessages()
+    
+    boolean assertContains(String text)
+    boolean assertNotContains(String text)
+    boolean assertRegex(String regex)
+}
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