feat(layout): add measure_font_crispness — verify a ladder rung isn't blurry

PIL antialiases TTF outlines by default; a 'pixel-style' font only
rasterizes without antialiasing at specific sizes (for PressStart2P:
exact multiples of its 8px design grid). A ladder rung at an unverified
size silently renders blurry on an LED panel — this exact bug shipped in
both text-display's and football-scoreboard's custom TTF ladders
(non-8-multiple PressStart2P sizes, and '5by7.regular'/'4x6-font' at
sizes that were never actually crisp).

measure_font_crispness(font, sample_text) renders the sample and reports
the fraction of ink-bbox pixels that are neither pure black nor pure
white. BDF fonts (real bitmaps) always score 0.0; TTF ladders should be
verified against this before shipping — see the new
TestFontFitting::test_ladder_arcade_is_crisp pattern.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/test_adaptive_layout.py

@@ -9,6 +9,7 @@ from src.adaptive_layout import (
     LayoutContext,
     Region,
     draw_fitted_text,
+    measure_font_crispness,
     measure_ink,
     media_row,
     scoreboard_regions,
@@ -182,6 +183,27 @@ class TestFontFitting:
             assert heights == sorted(heights, reverse=True), (
                 f"ladder not monotonically shrinking: {heights}")
 
+    def test_ladder_grid_is_crisp(self, font_manager):
+        """LADDER_GRID's BDF fonts are real bitmaps — always 0% antialiased."""
+        for step in LADDER_GRID:
+            font = font_manager.get_font(step.family, step.size_px)
+            assert measure_font_crispness(font, "Ay0") == 0.0
+
+    def test_ladder_arcade_is_crisp(self, font_manager):
+        """PressStart2P only rasterizes without antialiasing at exact
+        multiples of its 8px design grid — every LADDER_ARCADE rung must
+        land on one."""
+        for step in LADDER_ARCADE:
+            assert step.size_px % 8 == 0, f"{step} is not a multiple of 8"
+            font = font_manager.get_font(step.family, step.size_px)
+            assert measure_font_crispness(font, "17-21") == 0.0
+
+    def test_crispness_catches_a_bad_size(self, font_manager):
+        """Sanity check the measurement itself: a known-bad size for a
+        pixel-grid font must NOT read as crisp."""
+        font = font_manager.get_font("press_start", 10)  # not a multiple of 8
+        assert measure_font_crispness(font, "17-21") > 0.1
+
     def test_fit_text_grows_on_taller_panel(self, font_manager):
         small = LayoutContext(64, 32, font_manager)
         large = LayoutContext(128, 64, font_manager)