fix: use a real bold system font instead of Pillow's default face

Pillow's load_default() font is a thin geometric face that renders
mushy at small pixel sizes even with a stroke faking boldness. Look
up a proper hinted bold font (Liberation Sans / DejaVu Sans Bold,
common Linux/Windows/macOS paths) and use it directly; fall back to
load_default() with the old stroke trick only if none is found.

_label_ops.py

@@ -5,6 +5,8 @@ Shared by the node's own execution (`labeled_load_image_node.py`) and the
 to what actually gets queued - one implementation, not two.
 """
 
+import os
+
 from PIL import Image as PILImage
 from PIL import ImageDraw, ImageFont
 
@@ -14,6 +16,47 @@ ARROW_ZONE_RATIO = 0.4
 MIN_FONT_PX = 16
 TEXT_WIDTH_RATIO = 0.92
 
+# Pillow's own load_default() font is a thin geometric face that reads mushy
+# at small pixel sizes even with a stroke faking boldness. A real hinted bold
+# font looks crisp at the same size, so prefer whichever of these the host
+# actually has installed - common Linux/Windows/macOS bold sans paths, most
+# widely available first. Falls back to load_default() if none exist.
+_BOLD_FONT_CANDIDATES = (
+    "/usr/share/fonts/liberation/LiberationSans-Bold.ttf",
+    "/usr/share/fonts/liberation-fonts/LiberationSans-Bold.ttf",
+    "/usr/share/fonts/truetype/liberation/LiberationSans-Bold.ttf",
+    "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",
+    "/usr/share/fonts/TTF/DejaVuSans-Bold.ttf",
+    "/usr/share/fonts/dejavu/DejaVuSans-Bold.ttf",
+    "C:\\Windows\\Fonts\\arialbd.ttf",
+    "C:\\Windows\\Fonts\\seguisb.ttf",
+    "/System/Library/Fonts/Supplemental/Arial Bold.ttf",
+    "/Library/Fonts/Arial Bold.ttf",
+)
+
+_bold_font_path = None
+_bold_font_path_checked = False
+
+
+def _find_bold_font_path():
+    global _bold_font_path, _bold_font_path_checked
+    if not _bold_font_path_checked:
+        _bold_font_path_checked = True
+        for path in _BOLD_FONT_CANDIDATES:
+            if os.path.isfile(path):
+                _bold_font_path = path
+                break
+    return _bold_font_path
+
+
+def _load_font(size):
+    """Returns (font, is_real_bold_face). Caller uses the flag to decide
+    whether a stroke is still needed to fake boldness."""
+    path = _find_bold_font_path()
+    if path:
+        return ImageFont.truetype(path, size), True
+    return ImageFont.load_default(size=size), False
+
 
 def _hex_to_rgb(hex_str, fallback=(0, 0, 0)):
     if not isinstance(hex_str, str):
@@ -29,15 +72,15 @@ def _hex_to_rgb(hex_str, fallback=(0, 0, 0)):
 
 def _fit_text(draw, text, max_width, max_font_px):
     """Shrinks font size to fit max_width, then truncates with an ellipsis if
-    even the floor size overflows. Returns (font, drawn_text)."""
+    even the floor size overflows. Returns (font, is_bold_face, drawn_text)."""
     size = max(MIN_FONT_PX, max_font_px)
-    font = ImageFont.load_default(size=size)
+    font, is_bold = _load_font(size)
     while size > MIN_FONT_PX and draw.textlength(text, font=font) > max_width:
         size -= 1
-        font = ImageFont.load_default(size=size)
+        font, is_bold = _load_font(size)
 
     if draw.textlength(text, font=font) <= max_width:
-        return font, text
+        return font, is_bold, text
 
     lo, hi = 0, len(text)
     while lo < hi:
@@ -47,7 +90,7 @@ def _fit_text(draw, text, max_width, max_font_px):
             lo = mid
         else:
             hi = mid - 1
-    return font, (text[:lo] + "…" if lo > 0 else "…")
+    return font, is_bold, (text[:lo] + "…" if lo > 0 else "…")
 
 
 def _draw_arrow(draw, center_x, zone_top, zone_h, point_down, color_rgb):
@@ -109,8 +152,10 @@ def compose_labeled_image(img, text, position, show_label, show_arrow,
 
         if show_label and text:
             max_font_px = max(MIN_FONT_PX, round(text_zone_h * 0.62))
-            font, shown = _fit_text(draw, text, width * TEXT_WIDTH_RATIO, max_font_px)
-            stroke_width = max(1, round(font.size / 18))
+            font, is_bold, shown = _fit_text(draw, text, width * TEXT_WIDTH_RATIO, max_font_px)
+            # Already a bold face: no stroke, it would just clog up small glyphs.
+            # Fallback face has no bold weight: fake it with a thin stroke instead.
+            stroke_width = 0 if is_bold else max(1, round(font.size / 18))
             draw.text(
                 (width / 2, text_zone_top + text_zone_h / 2),
                 shown, font=font, fill=text_rgb, stroke_width=stroke_width,