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/Tactility.cpp

@@ -151,6 +151,8 @@ namespace app {
     namespace apwebserver { extern const AppManifest manifest; }
     namespace crashdiagnostics { extern const AppManifest manifest; }
     namespace webserversettings { extern const AppManifest manifest; }
+    namespace mcpsettings { extern const AppManifest manifest; }
+    namespace mcpoverride { extern const AppManifest manifest; }
 #if CONFIG_TT_TDECK_WORKAROUND == 1
     namespace keyboardsettings { extern const AppManifest manifest; } // T-Deck only for now
     namespace trackballsettings { extern const AppManifest manifest; } // T-Deck only for now
@@ -213,6 +215,8 @@ static void registerInternalApps() {
 #ifdef ESP_PLATFORM
     addAppManifest(app::apwebserver::manifest);
     addAppManifest(app::webserversettings::manifest);
+    addAppManifest(app::mcpsettings::manifest);
+    addAppManifest(app::mcpoverride::manifest);
     addAppManifest(app::crashdiagnostics::manifest);
     addAppManifest(app::development::manifest);
 #if defined(CONFIG_TT_TDECK_WORKAROUND)