Add MCP bridge for external tool integration

Embedded JSON-RPC server over named pipes (rcx-mcp) enabling external
tools like Claude Code to inspect and manipulate the node tree, read/write
hex data, switch sources, and trigger UI actions. Includes stdio adapter
(rcx-mcp-stdio) for stdin/stdout transport. Server is stopped by default;
user starts via File > Start MCP Server.

Also extracts MainWindow class declaration to mainwindow.h and improves
type selector popup Esc button styling.

src/controller.h

@@ -110,6 +110,12 @@ public:
     RcxDocument* document() const { return m_doc; }
     void setEditorFont(const QString& fontName);
 
+    // MCP bridge accessors
+    void setSuppressRefresh(bool v) { m_suppressRefresh = v; }
+    const QVector<SavedSourceEntry>& savedSources() const { return m_savedSources; }
+    int activeSourceIndex() const { return m_activeSourceIdx; }
+    void switchSource(int idx) { switchToSavedSource(idx); }
+
 signals:
     void nodeSelected(int nodeIdx);
     void selectionChanged(int count);