feat(cover): pixel-width headline truncation and larger font

Replace character-count truncation (45 chars) with Pillow textbbox
pixel-width measurement. Bump headline font 14→18, line spacing 22→26.

Made-with: Cursor

tests/test_cover.py

@@ -3,13 +3,15 @@ from collections import Counter
 from datetime import date
 from unittest.mock import patch, MagicMock
 from io import BytesIO
-from PIL import Image as PILImage
+from PIL import Image as PILImage, ImageDraw, ImageFont
 
 from src.cover import (
     generate_programmatic_cover,
     generate_ai_cover,
     generate_cover,
     _get_dominant_category,
+    _truncate_to_width,
+    _get_font,
     CATEGORY_PROMPTS,
 )
 
@@ -109,3 +111,28 @@ def test_get_dominant_category():
 def test_category_prompts_include_massachusetts():
     for category, prompt in CATEGORY_PROMPTS.items():
         assert "Massachusetts" in prompt, f"Prompt for {category} missing 'Massachusetts'"
+
+
+def test_truncate_to_width_respects_pixel_budget():
+    font = _get_font(18)
+    short = "Short text"
+    result = _truncate_to_width(short, font, 400)
+    assert result == short, "Short text should not be truncated"
+
+    long = "A" * 200
+    result = _truncate_to_width(long, font, 400)
+    assert result.endswith("\u2026"), "Long text should end with ellipsis"
+    assert len(result) < len(long), "Truncated text should be shorter"
+
+
+def test_truncate_to_width_fits_within_budget():
+    font = _get_font(18)
+    long = "This is a really long headline that should definitely be truncated to fit"
+    max_width = 448
+    result = _truncate_to_width(long, font, max_width)
+
+    dummy = PILImage.new("RGBA", (1, 1))
+    draw = ImageDraw.Draw(dummy)
+    bbox = draw.textbbox((0, 0), result, font=font)
+    rendered_width = bbox[2] - bbox[0]
+    assert rendered_width <= max_width, f"Rendered width {rendered_width} exceeds {max_width}"