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/Source/settings/McpSettings.cpp

@@ -0,0 +1,72 @@
+#include <Tactility/settings/McpSettings.h>
+#include <Tactility/file/PropertiesFile.h>
+#include <Tactility/file/File.h>
+#include <tactility/log.h>
+
+constexpr auto* TAG = "McpSettings";
+#include <Tactility/Paths.h>
+#include <map>
+#include <string>
+
+namespace tt::settings::mcp {
+
+
+static std::string getSettingsFilePath() {
+    return getUserDataPath() + "/settings/mcp.properties";
+}
+
+constexpr auto* KEY_MCP_ENABLED = "mcpEnabled";
+
+bool load(McpSettings& settings) {
+    auto settings_path = getSettingsFilePath();
+    if (!file::isFile(settings_path)) {
+        return false;
+    }
+    std::map<std::string, std::string> map;
+    if (!file::loadPropertiesFile(settings_path, map)) {
+        return false;
+    }
+
+    auto mcp_enabled = map.find(KEY_MCP_ENABLED);
+    settings.mcpEnabled = (mcp_enabled != map.end())
+        ? (mcp_enabled->second == "1" || mcp_enabled->second == "true")
+        : false;
+
+    return true;
+}
+
+McpSettings getDefault() {
+    return McpSettings{
+        .mcpEnabled = false
+    };
+}
+
+McpSettings loadOrGetDefault() {
+    McpSettings settings;
+    if (!load(settings)) {
+        settings = getDefault();
+        if (!save(settings)) {
+            LOG_W(TAG, "Failed to save default MCP settings");
+        }
+    }
+    return settings;
+}
+
+bool save(const McpSettings& settings) {
+    std::map<std::string, std::string> map;
+    map[KEY_MCP_ENABLED] = settings.mcpEnabled ? "true" : "false";
+
+    auto settings_path = getSettingsFilePath();
+    if (!file::findOrCreateParentDirectory(settings_path, 0755)) {
+        LOG_E(TAG, "Failed to create parent dir for %s", settings_path.c_str());
+        return false;
+    }
+
+    if (!file::savePropertiesFile(settings_path, map)) {
+        LOG_E(TAG, "Failed to save MCP settings to %s", settings_path.c_str());
+        return false;
+    }
+    return true;
+}
+
+} // namespace