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/gtk_utils.py

@@ -3,7 +3,14 @@ import struct
 from pathlib import Path
 from typing import Literal
 
-from fabric.utils import Gdk, GLib, bulk_connect, exec_shell_command_async, logger
+from fabric.utils import (
+    Gdk,
+    GdkPixbuf,
+    GLib,
+    bulk_connect,
+    exec_shell_command_async,
+    logger,
+)
 from fabric.widgets.svg import Svg
 
 
@@ -168,3 +175,21 @@ class EvdevLEDMonitor:
             except OSError as e:
                 logger.warning(f"[utils] os.close(self._fd) failed: {e}")
             self._fd = None
+
+
+def load_pixbuf_thumbnail(
+    path: str, width: int, height: int, *, fallback: str | None = None
+) -> GdkPixbuf.Pixbuf | None:
+    """Load a pixbuf scaled to fit within *width* x *height*.
+
+    Returns ``None`` on failure (file missing, corrupt, etc.).  Pass a
+    *fallback* path to try that on failure too.
+    """
+    for p in (path, fallback):
+        if p is None:
+            continue
+        try:
+            return GdkPixbuf.Pixbuf.new_from_file_at_scale(p, width, height, True)
+        except Exception as e:
+            logger.warning(f"[gtk_utils] Failed to load pixbuf from {p}: {e}")
+    return None