feat(2-6): stateful Renderer, DisplayInterface, and pipeline smoke test

Implements story 2-6: Renderer class with per-aircraft trail history
(deque capped at TRAIL_MAX_DOTS=5), NullDisplay with DEBUG logging,
WaveshareDisplay stub, and end-to-end pipeline smoke test. All 96
tests pass; ruff check and format clean.

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

src/planemapper/display.py

@@ -1,7 +1,12 @@
+from __future__ import annotations
+
+import logging
 from typing import Protocol
 
 from PIL import Image
 
+log = logging.getLogger(__name__)
+
 
 class DisplayInterface(Protocol):
     def show(self, image: Image.Image) -> None: ...
@@ -9,4 +14,9 @@ class DisplayInterface(Protocol):
 
 class NullDisplay:
     def show(self, image: Image.Image) -> None:
-        pass
+        log.debug("NullDisplay.show: %dx%d", image.width, image.height)
+
+
+class WaveshareDisplay:
+    def show(self, image: Image.Image) -> None:
+        raise NotImplementedError

src/planemapper/renderer/renderer.py

@@ -1 +1,33 @@
-# stub
+from __future__ import annotations
+
+import collections
+
+from PIL import Image
+
+from planemapper.constants import TRAIL_MAX_DOTS
+from planemapper.models import Aircraft
+from planemapper.renderer.aircraft import draw_aircraft
+from planemapper.renderer.airspace import draw_airspace
+from planemapper.renderer.overlay import draw_home_marker
+from planemapper.renderer.projection import MapBounds, project
+
+
+class Renderer:
+    def __init__(self, base_map: Image.Image, bounds: MapBounds) -> None:
+        self._base_map = base_map
+        self._bounds = bounds
+        self._trails: dict[str, collections.deque[tuple[int, int]]] = {}
+
+    def render(self, aircraft_list: list[Aircraft]) -> Image.Image:
+        image = self._base_map.copy()
+        draw_airspace(image, self._bounds)
+        draw_home_marker(image, self._bounds)
+        for aircraft in aircraft_list:
+            pos = project(aircraft.lat, aircraft.lon, self._bounds)
+            trail = self._trails.get(aircraft.icao, collections.deque())
+            draw_aircraft(image, aircraft, pos, trail)
+            trail.appendleft(pos)
+            while len(trail) > TRAIL_MAX_DOTS:
+                trail.pop()
+            self._trails[aircraft.icao] = trail
+        return image