feat: implement MCP drawing as screensaver instead of standalone app

- Add ScreensaverType::McpScreen to DisplaySettings enum, toString/fromString
- Add 'MCP Screen' option to the Display settings screensaver dropdown
- New McpScreensaver (Screensaver subclass): creates full-screen lv_canvas on
  the overlay, allocates framebuffer in SPIRAM, registers canvas pointer in
  McpSystemState, shows 'Waiting for LLM...' until first draw command arrives
- Wire McpScreensaver into DisplayIdle::activateScreensaver() switch
- McpSystem::ensureOverrideScreen() now calls displayidle::findService()->
  startScreensaver() instead of launching McpOverrideApp — canvas appears
  automatically on any LLM draw command
- Remove McpOverrideApp (replaced by screensaver), deregister from Tactility.cpp
- Remove mcpOverrideEnabled from McpSettings — no longer needed
- Simplify McpSettingsApp: remove Screen Override toggle, update info text to
  direct users to Settings -> Display -> Screensaver -> MCP Screen

Tactility/Source/service/displayidle/DisplayIdle.cpp

@@ -7,6 +7,7 @@
 #include "MatrixRainScreensaver.h"
 #include "MystifyScreensaver.h"
 #include "StackChanScreensaver.h"
+#include "McpScreensaver.h"
 
 #include <Tactility/Logger.h>
 #include <Tactility/CoreDefines.h>
@@ -103,6 +104,9 @@ void DisplayIdleService::activateScreensaver() {
         case settings::display::ScreensaverType::StackChan:
             screensaver = std::make_unique<StackChanScreensaver>();
             break;
+        case settings::display::ScreensaverType::McpScreen:
+            screensaver = std::make_unique<McpScreensaver>();
+            break;
         case settings::display::ScreensaverType::None:
         default:
             // Just black screen, no animated screensaver

Tactility/Source/service/displayidle/McpScreensaver.cpp

@@ -0,0 +1,98 @@
+#ifdef ESP_PLATFORM
+
+#include "McpScreensaver.h"
+#include <Tactility/mcp/McpSystem.h>
+#include <Tactility/Logger.h>
+#include <esp_heap_caps.h>
+
+namespace tt::service::displayidle {
+
+static const auto LOGGER = Logger("McpScreensaver");
+
+void McpScreensaver::start(lv_obj_t* overlay, lv_coord_t screenW, lv_coord_t screenH) {
+    auto& state = mcp::getState();
+
+    // Full-screen canvas on the overlay
+    lv_obj_t* canvas = lv_canvas_create(overlay);
+    lv_obj_set_size(canvas, screenW, screenH);
+    lv_obj_set_pos(canvas, 0, 0);
+    lv_obj_set_style_radius(canvas, 0, LV_PART_MAIN);
+    lv_obj_set_style_border_width(canvas, 0, LV_PART_MAIN);
+    lv_obj_set_style_pad_all(canvas, 0, LV_PART_MAIN);
+    lv_obj_remove_flag(canvas, LV_OBJ_FLAG_SCROLLABLE);
+
+    // Allocate framebuffer (prefer SPIRAM)
+    size_t requiredSize = (size_t)screenW * screenH * sizeof(uint16_t);
+    framebuffer = (uint16_t*)heap_caps_malloc(requiredSize, MALLOC_CAP_SPIRAM | MALLOC_CAP_8BIT);
+    if (framebuffer == nullptr) {
+        framebuffer = (uint16_t*)heap_caps_malloc(requiredSize, MALLOC_CAP_8BIT);
+    }
+    framebufferSize = (framebuffer != nullptr) ? requiredSize : 0;
+
+    if (framebuffer == nullptr) {
+        LOGGER.error("Failed to allocate {}B framebuffer", (unsigned)requiredSize);
+        lv_obj_t* err = lv_label_create(canvas);
+        lv_label_set_text(err, "Framebuffer alloc failed");
+        lv_obj_center(err);
+        return;
+    }
+
+    // Fill with a dark slate background
+    size_t pixelCount = (size_t)screenW * screenH;
+    for (size_t i = 0; i < pixelCount; ++i) {
+        framebuffer[i] = 0x18E3; // dark blue-grey
+    }
+
+    lv_canvas_set_buffer(canvas, framebuffer, screenW, screenH, LV_COLOR_FORMAT_RGB565);
+
+    // Waiting label (removed on first MCP draw via lv_obj_clean)
+    lv_obj_t* waitLabel = lv_label_create(canvas);
+    lv_label_set_text(waitLabel, "Waiting for LLM...");
+    lv_obj_set_style_text_color(waitLabel, lv_color_white(), LV_PART_MAIN);
+    lv_obj_align(waitLabel, LV_ALIGN_CENTER, 0, -20);
+
+    lv_obj_t* resLabel = lv_label_create(canvas);
+    lv_label_set_text_fmt(resLabel, "Display: %dx%d", (int)screenW, (int)screenH);
+    lv_obj_set_style_text_color(resLabel, lv_palette_lighten(LV_PALETTE_BLUE, 3), LV_PART_MAIN);
+    lv_obj_align(resLabel, LV_ALIGN_CENTER, 0, 10);
+
+    // Register with McpSystemState
+    std::lock_guard<std::mutex> lock(state.mutex);
+    state.drawArea = canvas;
+    state.framebuffer = framebuffer;
+    state.framebufferSize = framebufferSize;
+    state.displayWidth = (uint16_t)screenW;
+    state.displayHeight = (uint16_t)screenH;
+    state.drawWidth = (uint16_t)screenW;
+    state.drawHeight = (uint16_t)screenH;
+    // Don't reset overrideActive — if the LLM already drew, we keep the content
+
+    LOGGER.info("McpScreensaver started ({}x{})", (int)screenW, (int)screenH);
+}
+
+void McpScreensaver::stop() {
+    auto& state = mcp::getState();
+    {
+        std::lock_guard<std::mutex> lock(state.mutex);
+        state.drawArea = nullptr;
+        state.framebuffer = nullptr;
+        state.framebufferSize = 0;
+        state.overrideActive = false;
+    }
+
+    if (framebuffer != nullptr) {
+        heap_caps_free(framebuffer);
+        framebuffer = nullptr;
+        framebufferSize = 0;
+    }
+
+    LOGGER.info("McpScreensaver stopped");
+}
+
+void McpScreensaver::update(lv_coord_t /*screenW*/, lv_coord_t /*screenH*/) {
+    // MCP draws on demand via HTTP — no per-frame animation needed
+}
+
+} // namespace tt::service::displayidle
+
+#endif // ESP_PLATFORM

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