fix: MCP settings persistence + WebServer/DevServer coexistence + screensaver charging toggle

- McpSettings was hardcoded to /data/service/mcp/settings.properties,
  but ES3C28P uses storage.userDataLocation=SD so user data lives on
  /sdcard/tactility/. Settings appeared to save but on reload returned
  default false -> "enable and when I go back shows disabled".
  Fixed to use getUserDataPath()+"/settings/mcp.properties" pattern
  consistent with DisplaySettings/WebServerSettings, with
  findOrCreateParentDirectory() and isFile() guard.

- HttpServer ctrl_port collision: ESP-IDF default 32768 used by both
  WebServer (80) and DevelopmentService (6666). Second httpd_start()
  failed silently -> dashboard up but /api/mcp 404 and :6666 refused.
  Fixed with unique ctrl_port = 32768 + (port % 1000).
  Added CONFIG_HTTPD_MAX_URI_HANDLERS=20 (default 8 < 9 needed for
  7 handlers + 2 internal).

- DevService stack 5120 -> 8192 for /app/install handling.
- McpSystem video stream task stack 4096 -> 8192 and idle yield 50ms
  (was 5ms always) to avoid CPU starvation blocking httpd tasks.
  On RLCD, timer must always run: DisplayIdle early return on
  !supportsBacklightDuty() broke MCP manual activation (cachedSettings
  not loaded, backlight duty 0). Fixed to always load settings +
  start timer, log RLCD detection, guard setBacklightDuty with
  supportsBacklightDuty() and fallback duty 255.

- DisplaySettings: add disableScreensaverWhenCharging bool, persisted,
  with UI toggle in Display app (Settings->Display) using
  PowerDevice::IsCharging check via findDevices callback.
  When charging and flag enabled, screensaver activation skipped,
  and if already dimmed, wake on charging.

- ES3C28P Power driver: GPIO9 ADC1_CH8 2x divider 2500-4200mV spec from
  ~/Downloads official docs, TP4054 CHRG not connected to GPIO, so
  IsCharging inferred via voltage thresholds (<500mV no battery USB
  or >5000mV wall powered, >=4150mV high) + rising trend.

Verified: flashed es3c28p to /dev/cu.usbmodem101 (192.168.68.113),
WiFi FamReynaMesh RSSI -59, dashboard 200, :6666/info now works,
/api/mcp returns disabled correctly until enabled, persists to SD.

Buildscripts/sdkconfig/default.properties

@@ -2,6 +2,8 @@
 CONFIG_ESP_SYSTEM_EVENT_TASK_STACK_SIZE=3072
 # Ensure large enough stack for network operations
 CONFIG_ESP_MAIN_TASK_STACK_SIZE=6144
+# HTTP server: need enough URI handler slots for WebServer (7 + internal) + DevServer
+CONFIG_HTTPD_MAX_URI_HANDLERS=20
 # Fixes static assertion: FLASH and PSRAM Mode configuration are not supported
 CONFIG_IDF_EXPERIMENTAL_FEATURES=y
 # Free up IRAM