feat(mcp): restore MCP service with display charging toggle

- Restore MCP system (McpSystem 1900+ LOC, McpHandler, McpScreensaver, McpSettings, McpOverride apps)
- Use audio-stream instead of direct I2S for MP3 playback (fixes fast playback, uses native resampler)
- Register McpSettings + McpOverride in Tactility.cpp so Settings shows MCP Screen
- DisplaySettings: add ScreensaverType::McpScreen and disableScreensaverWhenCharging flag
- Display app: add 'Disable on charging' toggle, handles McpScreen screensaver type
- DisplayIdle: skip screensaver while charging, support McpScreen screensaver, isDeviceCharging check via PowerDevice
- WebServer: coexistence with MCP (McpHandler)
- Avoid formatting churn from previous commits

Squashed from range eaa248b0..8970143f (6 commits) into single clean commit

Tactility/Private/Tactility/mcp/McpSystem.h

@@ -0,0 +1,77 @@
+#pragma once
+#ifdef ESP_PLATFORM
+
+#include <lvgl.h>
+#include <mutex>
+#include <string>
+#include <vector>
+#include <tactility/device.h>
+#include <tactility/drivers/audio_stream.h>
+
+namespace tt::mcp {
+
+struct McpSystemState {
+    std::mutex mutex;
+    bool overrideActive = false;
+    
+    // UI elements when McpOverrideApp is active
+    lv_obj_t* drawArea = nullptr;
+    uint16_t* framebuffer = nullptr;
+    size_t framebufferSize = 0;
+    uint16_t displayWidth = 320;
+    uint16_t displayHeight = 240;
+    uint16_t drawWidth = 320;
+    uint16_t drawHeight = 240;
+    int drawColor = 1; // 0 = white, 1 = black
+    
+    // Audio device status
+    Device* i2sDevice = nullptr;
+    Device* audioStreamDevice = nullptr;
+    AudioStreamHandle audioHandle = nullptr;
+    volatile bool audioBusy = false;
+    volatile bool audioRunning = false; // Used to abort play/record loop
+
+    // Video streaming state
+    volatile bool streamRunning = false;
+    void* streamTaskHandle = nullptr; // use void* to avoid freertos header inclusion dependency
+    uint32_t framesDrawn = 0;
+    uint32_t tcpBytesReceived = 0;
+    uint32_t lastDrawMs = 0;
+    double lastFps = 0.0;
+};
+
+McpSystemState& getState();
+
+bool clearScreen(int color);
+bool drawText(const std::string& text, int x, int y, int size);
+bool drawRgb565(const uint8_t* data, size_t size, int x, int y, int w, int h);
+bool drawBmp(const uint8_t* data, size_t size, int x, int y);
+bool drawPbm(const uint8_t* data, size_t size, int x, int y);
+std::string getScreenshotPbmBase64();
+
+bool playTone(int frequency, int durationMs, int volume, std::string& error);
+bool recordVoice(int durationSec, const std::string& filename, size_t& recordedBytes, std::string& error);
+bool playAudioFile(const std::string& filename, int volume, std::string& error);
+bool playWavMemory(const uint8_t* data, size_t size, int volume, std::string& error);
+bool playMp3File(const std::string& filename, int volume, std::string& error);
+bool playMp3Memory(const uint8_t* data, size_t size, int volume, std::string& error);
+
+bool getBatteryStatus(double& voltage_v, int& percentage_pct, std::string& error);
+bool setLedColor(int r, int g, int b, const std::string& mode, std::string& error);
+bool getSensors(double& temp_c, double& hum_pct, std::string& imu_json, std::string& error);
+bool scanBleDevices(int duration_ms, std::string& devices_json, std::string& error);
+bool writeSdFile(const std::string& filename, const std::string& content, std::string& error);
+bool readSdFile(const std::string& filename, std::string& content, std::string& error);
+bool downloadSdFile(const std::string& url, const std::string& filename, std::string& error);
+
+bool startVideoStreamServer();
+void stopVideoStreamServer();
+bool getVideoStreamStats(std::string& stats_json);
+
+bool listApps(std::string& apps_json, std::string& error);
+bool runApp(const std::string& appId, std::string& error);
+bool listSdFiles(const std::string& directory, std::string& files_json, std::string& error);
+
+} // namespace tt::mcp
+
+#endif

Tactility/Private/Tactility/service/displayidle/DisplayIdleService.h

@@ -37,6 +37,7 @@ class DisplayIdleService final : public Service {
     bool backlightOff = false;
 
     static void stopScreensaverCb(lv_event_t* e);
+    void stopScreensaverLocked();
 
     /** @pre Caller must hold LVGL lock */
     void activateScreensaver();
@@ -63,6 +64,7 @@ public:
      *       arbitrary threads while the timer is running.
      */
     void stopScreensaver();
+    void startMcpScreensaver();
 
     /**
      * Check if the screensaver is currently active.

Tactility/Private/Tactility/service/webserver/WebServerService.h

@@ -76,6 +76,8 @@ private:
     static esp_err_t handleApiAppsInstall(httpd_req_t* request);
     static esp_err_t handleApiWifi(httpd_req_t* request);
     static esp_err_t handleApiScreenshot(httpd_req_t* request);
+    static esp_err_t handleApiMcp(httpd_req_t* request);
+    static esp_err_t handleApiScreenRaw(httpd_req_t* request);
 
     // Dynamic asset serving
     static esp_err_t handleAssets(httpd_req_t* request);