feat(renderer): implement per-aircraft drawing — story 2-5

Implements draw_aircraft() with heading arrow (filled/outlined for MLAT),
callsign+altitude label, and a 5-dot fade trail. Adds 5 tests covering
all ACs; all 94 tests pass, ruff lint and format clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_aircraft_draw.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+import collections
+
+from PIL import Image
+
+from planemapper.models import Aircraft
+from planemapper.renderer.aircraft import draw_aircraft
+
+
+def _white_image() -> Image.Image:
+    return Image.new("RGB", (800, 480), color=(255, 255, 255))
+
+
+def _aircraft(**kwargs) -> Aircraft:
+    defaults = {"icao": "ABC123", "lat": 53.0, "lon": -6.0}
+    defaults.update(kwargs)
+    return Aircraft(**defaults)
+
+
+def test_heading_east_changes_pixels() -> None:
+    img = _white_image()
+    ac = _aircraft(heading=90.0, altitude_ft=10000)
+    draw_aircraft(img, ac, (400, 240), collections.deque())
+    # Arrow should have painted at least one non-white pixel near centre
+    changed = any(
+        img.getpixel((x, y)) != (255, 255, 255) for x in range(388, 413) for y in range(228, 253)
+    )
+    assert changed
+
+
+def test_label_with_callsign_no_exception() -> None:
+    img = _white_image()
+    ac = _aircraft(callsign="BAW1", altitude_ft=28000)
+    result = draw_aircraft(img, ac, (400, 240), collections.deque())
+    assert result is None
+
+
+def test_trail_drawn_no_exception() -> None:
+    img = _white_image()
+    ac = _aircraft(altitude_ft=5000)
+    trail: collections.deque[tuple[int, int]] = collections.deque(
+        [(390, 230), (380, 220), (370, 210)]
+    )
+    result = draw_aircraft(img, ac, (400, 240), trail)
+    assert result is None
+
+
+def test_mlat_aircraft_no_exception() -> None:
+    img = _white_image()
+    ac = _aircraft(is_mlat=True, altitude_ft=8000)
+    result = draw_aircraft(img, ac, (400, 240), collections.deque())
+    assert result is None
+
+
+def test_empty_callsign_no_exception() -> None:
+    img = _white_image()
+    ac = _aircraft(callsign="", altitude_ft=15000)
+    result = draw_aircraft(img, ac, (400, 240), collections.deque())
+    assert result is None