feat(mcp): restore MCP system with native log.h

- MCP 3.3K LOC: McpSystem 1899 + McpHandler 1029 + McpScreensaver + 2 apps
- Uses native tactility/log.h TAG macros, no old Logger.h
- DisplaySettings McpScreen enum, WebServer coexistence (MCP enabled starts HTTP)
- DisplayIdle: startMcpScreensaver + isDeviceCharging + lock inversion fix 3629ffef
- LVGL 512K PSRAM cache retained from previous perf patch
- Audio kept upstream es8311-module per note we might not need custom

Tactility/Source/service/displayidle/McpScreensaver.h

@@ -0,0 +1,30 @@
+#pragma once
+#ifdef ESP_PLATFORM
+
+#include "Screensaver.h"
+#include <cstdint>
+
+namespace tt::service::displayidle {
+
+/**
+ * MCP Screen screensaver.
+ * Creates a full-screen LVGL canvas on the overlay and registers it in
+ * McpSystemState so that MCP HTTP draw commands can paint to it.
+ * Dismissed by a touch event (handled by the parent DisplayIdle overlay).
+ */
+class McpScreensaver final : public Screensaver {
+    uint16_t* framebuffer = nullptr;
+    size_t framebufferSize = 0;
+
+public:
+    McpScreensaver() = default;
+    ~McpScreensaver() override = default;
+
+    void start(lv_obj_t* overlay, lv_coord_t screenW, lv_coord_t screenH) override;
+    void stop() override;
+    void update(lv_coord_t screenW, lv_coord_t screenH) override;
+};
+
+} // namespace tt::service::displayidle
+
+#endif // ESP_PLATFORM