Refactor core/ into logical sub-packages and split filter files

Reorganize the flat core/ directory (17 files) into three sub-packages:
- core/devices/ — LED device communication (led_client, wled/adalight clients, providers, DDP)
- core/processing/ — target processing pipeline (processor_manager, target processors, live streams, settings)
- core/capture/ — screen capture & calibration (screen_capture, calibration, pixel_processor, overlay)

Also split the monolithic filters/builtin.py (460 lines, 8 filters) into
individual files: brightness, saturation, gamma, downscaler, pixelate,
auto_crop, flip, color_correction.

Includes the ProcessorManager refactor from target-centric architecture:
ProcessorManager slimmed from ~1600 to ~490 lines with unified
_processors dict replacing duplicate _targets/_kc_targets dicts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/main.py

@@ -13,7 +13,8 @@ from wled_controller import __version__
 from wled_controller.api import router
 from wled_controller.api.dependencies import init_dependencies
 from wled_controller.config import get_config
-from wled_controller.core.processor_manager import ProcessorManager, ProcessingSettings
+from wled_controller.core.processing.processor_manager import ProcessorManager
+from wled_controller.core.processing.processing_settings import ProcessingSettings
 from wled_controller.storage import DeviceStore
 from wled_controller.storage.template_store import TemplateStore
 from wled_controller.storage.postprocessing_template_store import PostprocessingTemplateStore
@@ -71,7 +72,7 @@ def _migrate_devices_to_targets():
             continue
 
         # Build ProcessingSettings from legacy data
-        from wled_controller.core.processor_manager import DEFAULT_STATE_CHECK_INTERVAL
+        from wled_controller.core.processing.processing_settings import DEFAULT_STATE_CHECK_INTERVAL
         settings = ProcessingSettings(
             display_index=legacy_settings.get("display_index", 0),
             fps=legacy_settings.get("fps", 30),
@@ -158,6 +159,7 @@ async def lifespan(app: FastAPI):
                 device_type=device.device_type,
                 baud_rate=device.baud_rate,
                 software_brightness=device.software_brightness,
+                auto_shutdown=device.auto_shutdown,
             )
             logger.info(f"Registered device: {device.name} ({device.id})")
         except Exception as e: