refactor: extract reusable utils, remove screencapture facade

- Add ManagedTimer to replace repeated source_remove/timeout_add boilerplate
- Add EvdevLockService base class for numlock/capslock (cut 154→28 lines)
- Add BaseNotchIndicator for 5 near-identical indicator classes (cut 404→171 lines)
- Add load_pixbuf_thumbnail and resolve_monitor to utils
- Delete screencapture.py facade; callers use Screenshot/ScreenRecorder directly

src/utils/evdev_lock.py

@@ -0,0 +1,90 @@
+"""Parameterised evdev LED-lock service base.
+
+NumLock and CapsLock services are structurally identical; only the LED
+glob pattern, LED index, and service name differ.  This module provides a
+single base class that both services can inherit from.
+"""
+
+from pathlib import Path
+
+from fabric.core.service import Property, Service, Signal
+from fabric.utils import logger
+
+from utils.gtk_utils import EvdevLEDMonitor
+
+
+class EvdevLockService(Service):
+    """Base service for keyboard lock-key monitoring via evdev LEDs.
+
+    Subclasses must set **class-level** attributes:
+
+    * ``_LED_GLOB`` – sysfs glob for the LED device
+      (e.g. ``"input*::numlock"``).
+    * ``_LED_INDEX`` – integer LED code passed to :class:`EvdevLEDMonitor`
+      (0 = NUML, 1 = CAPSL).
+    * ``_SERVICE_NAME`` – human-readable name for log messages.
+    """
+
+    _LED_GLOB: str = ""
+    _LED_INDEX: int = 0
+    _SERVICE_NAME: str = "EvdevLock"
+
+    _instance = None
+
+    @Signal
+    def state_changed(self, is_on: bool) -> None:
+        """Emitted when the lock-key state changes."""
+
+    def __new__(cls, *args, **kwargs):
+        if cls._instance is None:
+            cls._instance = super().__new__(cls)
+        return cls._instance
+
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+
+        leds = list(Path("/sys/class/leds").glob(self._LED_GLOB))
+        self._led_path = leds[0] if leds else None
+        self._last_state = None
+        self._monitoring_started = False
+
+        if self._led_path is None:
+            logger.warning(f"[{self._SERVICE_NAME}] Device not found, service disabled")
+            return
+
+        self._monitor = EvdevLEDMonitor(
+            self._led_path, self._LED_INDEX, self._on_state_changed
+        )
+
+    def _on_state_changed(self, is_on: bool):
+        if is_on != self._last_state:
+            self._last_state = is_on
+            self.emit("state_changed", is_on)
+
+    def stop(self):
+        if hasattr(self, "_monitor"):
+            self._monitor.stop()
+
+    def _ensure_monitoring_started(self):
+        if not self._monitoring_started and self._led_path:
+            self._monitoring_started = True
+            self._last_state = self._get_current_state()
+            self._monitor._last_state = self._last_state
+            self._monitor.start()
+
+    def _get_current_state(self) -> bool:
+        if not self._led_path:
+            return False
+        brightness_path = self._led_path / "brightness"
+        if brightness_path.exists():
+            try:
+                return bool(int(brightness_path.read_text().strip()))
+            except (ValueError, OSError) as e:
+                logger.warning(f"[{self._SERVICE_NAME}] Failed to read brightness: {e}")
+                return False
+        return False
+
+    @Property(bool, "read-write", default_value=False)
+    def is_on(self) -> bool:
+        self._ensure_monitoring_started()
+        return self._get_current_state()