feat: integrate MCP server and screen override into system firmware

- Add McpSettings (load/save mcpEnabled, mcpOverrideEnabled to /data/service/mcp/settings.properties)
- Add McpSystem: global state, canvas drawing (RGB565, BMP, PBM, text), I2S audio (WAV, MP3 via minimp3, tone, record)
- Add McpHandler: unauthenticated POST /api/mcp (JSON-RPC 2.0, 13 tools) and POST /api/screen/raw endpoints
- Route MCP endpoints before Basic Auth check in WebServerService::handleApiPost
- Start HTTP server at boot if either webServerEnabled OR mcpEnabled is set
- Fix setEnabled: start unconditionally when called with true; only stop if both WS and MCP are disabled
- Add McpSettingsApp (Settings category): toggle MCP service + screen override, show live endpoint URL
- Add McpOverrideApp (appId one.tactility.mcpscreen): full-screen LVGL canvas for LLM-driven display override
- Register both new apps in Tactility.cpp

Tactility/Private/Tactility/mcp/McpSystem.h

@@ -0,0 +1,50 @@
+#pragma once
+#ifdef ESP_PLATFORM
+
+#include <lvgl.h>
+#include <mutex>
+#include <string>
+#include <vector>
+#include <tactility/device.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;
+    volatile bool audioBusy = false;
+    volatile bool audioRunning = false; // Used to abort play/record loop
+};
+
+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);
+
+} // namespace tt::mcp
+
+#endif

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);