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>

src/planemapper/renderer/aircraft.py

@@ -1 +1,82 @@
-# stub
+from __future__ import annotations
+
+import collections
+import math
+
+from PIL import Image, ImageDraw, ImageFont
+
+from planemapper.constants import COLOUR_TRAIL, TRAIL_DOT_SIZE_MAX, TRAIL_DOT_SIZE_MIN
+from planemapper.models import Aircraft
+from planemapper.renderer.colours import altitude_to_colour
+
+
+def _rotate_point(x: float, y: float, angle_deg: float) -> tuple[float, float]:
+    r = math.radians(angle_deg)
+    return (x * math.cos(r) - y * math.sin(r), x * math.sin(r) + y * math.cos(r))
+
+
+def _draw_arrow(
+    draw: ImageDraw.ImageDraw,
+    cx: int,
+    cy: int,
+    heading: float,
+    colour: tuple[int, int, int],
+    is_mlat: bool,
+) -> None:
+    tip = _rotate_point(0, -12, heading)
+    left = _rotate_point(-6, 8, heading)
+    right = _rotate_point(6, 8, heading)
+    pts = [
+        (cx + tip[0], cy + tip[1]),
+        (cx + left[0], cy + left[1]),
+        (cx + right[0], cy + right[1]),
+    ]
+    if is_mlat:
+        draw.polygon(pts, fill=None, outline=colour)
+    else:
+        draw.polygon(pts, fill=colour)
+
+
+def _draw_label(
+    draw: ImageDraw.ImageDraw,
+    cx: int,
+    cy: int,
+    aircraft: Aircraft,
+    colour: tuple[int, int, int],
+) -> None:
+    font = ImageFont.load_default()
+    if aircraft.callsign:
+        text = f"{aircraft.callsign}\n{aircraft.altitude_ft}ft"
+    else:
+        text = f"{aircraft.altitude_ft}ft"
+    draw.text((cx + 12, cy - 8), text, fill=colour, font=font)
+
+
+def _draw_trail(
+    draw: ImageDraw.ImageDraw,
+    trail: collections.deque[tuple[int, int]],
+) -> None:
+    n = len(trail)
+    if n == 0:
+        return
+    for i, (tx, ty) in enumerate(trail):
+        if n > 1:
+            size = int(TRAIL_DOT_SIZE_MAX - i * (TRAIL_DOT_SIZE_MAX - TRAIL_DOT_SIZE_MIN) / (n - 1))
+        else:
+            size = TRAIL_DOT_SIZE_MAX
+        r = max(size // 2, 1)
+        draw.ellipse((tx - r, ty - r, tx + r, ty + r), fill=COLOUR_TRAIL)
+
+
+def draw_aircraft(
+    image: Image.Image,
+    aircraft: Aircraft,
+    pos: tuple[int, int],
+    trail: collections.deque[tuple[int, int]],
+) -> None:
+    cx, cy = pos
+    colour = altitude_to_colour(aircraft.altitude_ft)
+    draw = ImageDraw.Draw(image)
+    _draw_trail(draw, trail)
+    _draw_arrow(draw, cx, cy, aircraft.heading, colour, aircraft.is_mlat)
+    _draw_label(draw, cx, cy, aircraft, colour)