Journey: real train/bus pictograms instead of letter badges

Vendor Font Awesome Free Solid (fonts/fa-solid-900.ttf, SIL OFL
licensed -- see fonts/FONT-AWESOME-LICENSE.txt) for its actual
train/bus glyphs. Confirmed live these stay sharp and recognizable
even at the tiny size the detail line renders at (~20px), unlike a
hand-drawn shape would be, and unlike emoji (not in DejaVu Sans,
would've rendered as tofu).

render_utils.py gets a load_icon_font() alongside the existing
load_font(), plus named ICON_BUS/ICON_TRAIN codepoint constants so
screens don't need to embed raw Private-Use-Area unicode literals.

screens/render_utils.py

@@ -23,6 +23,22 @@ def load_font(size: int, bold: bool = False) -> ImageFont.FreeTypeFont:
     return _font_cache[key]
 
 
+# Font Awesome Free (Solid), vendored for real pictogram icons (train, bus,
+# etc.) where a hand-drawn shape or a plain letter would be less clear at a
+# glance than the real thing. SIL OFL licensed -- see fonts/FONT-AWESOME-LICENSE.txt.
+def load_icon_font(size: int) -> ImageFont.FreeTypeFont:
+    key = ("fa-solid", size)
+    if key not in _font_cache:
+        _font_cache[key] = ImageFont.truetype(str(FONTS_DIR / "fa-solid-900.ttf"), size)
+    return _font_cache[key]
+
+
+# Font Awesome Free Solid codepoints used by screens -- named here so callers
+# don't need to embed raw Private-Use-Area unicode literals.
+ICON_BUS = ""
+ICON_TRAIN = ""
+
+
 def text_width(draw, text: str, font: ImageFont.FreeTypeFont) -> int:
     left, _, right, _ = draw.textbbox((0, 0), text, font=font)
     return right - left