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/Source/Tactility.cpp

@@ -118,6 +118,8 @@ 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
@@ -167,6 +169,8 @@ 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)