Implement story 1.1: project scaffold and verified entry points

Creates the complete src/planemapper/ layout with all module stubs,
provisioning and renderer subpackages, airports.csv data bundle,
systemd unit files, and full test scaffold. All three quality gates
pass: pytest 12/12, ruff check zero violations, ruff format clean.

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

src/planemapper/constants.py

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+from pathlib import Path
+
+DISPLAY_WIDTH = 800
+DISPLAY_HEIGHT = 480
+
+REFRESH_INTERVAL_S = 60
+FETCH_TIMEOUT_S = 5
+RENDER_WARN_S = 40
+RENDER_ALERT_S = 50
+STALE_CYCLES = 1
+RESET_HOLD_S = 3
+
+ALTITUDE_BANDS_FT = [1500, 5000, 10000, 20000, 35000, 99999]
+
+COLOUR_BLACK = (0, 0, 0)
+COLOUR_WHITE = (255, 255, 255)
+COLOUR_RED = (255, 0, 0)
+COLOUR_YELLOW = (255, 255, 0)
+COLOUR_BLUE = (0, 0, 255)
+COLOUR_GREEN = (0, 255, 0)
+
+ALTITUDE_COLOURS = [
+    COLOUR_GREEN,
+    COLOUR_BLUE,
+    COLOUR_YELLOW,
+    COLOUR_RED,
+    COLOUR_BLACK,
+    COLOUR_WHITE,
+]
+
+COLOUR_STALE_OUTLINE = COLOUR_BLACK
+COLOUR_HOME_MARKER = COLOUR_RED
+COLOUR_AIRSPACE = COLOUR_BLUE
+COLOUR_TRAIL = COLOUR_BLACK
+
+TRAIL_MAX_DOTS = 5
+TRAIL_DOT_SIZE_MAX = 6
+TRAIL_DOT_SIZE_MIN = 2
+
+CONFIG_PATH = Path("/etc/planemapper/config.json")
+AIRSPACE_PATH = Path("/etc/planemapper/airspace.geojson")
+BACKGROUND_PATH = Path("/etc/planemapper/background.png")

src/planemapper/display.py

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+from typing import Protocol
+
+from PIL import Image
+
+
+class DisplayInterface(Protocol):
+    def show(self, image: Image.Image) -> None: ...
+
+
+class NullDisplay:
+    def show(self, image: Image.Image) -> None:
+        pass

src/planemapper/fetcher.py

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+from typing import Protocol
+
+from planemapper.models import Aircraft
+
+
+class FetcherInterface(Protocol):
+    def fetch(self) -> list[Aircraft]: ...

src/planemapper/gpio_ctrl.py

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+class ButtonHoldDetector:
+    def check(self) -> bool:
+        return False
+
+
+class LEDController:
+    def on(self) -> None:
+        pass
+
+    def off(self) -> None:
+        pass

src/planemapper/main.py

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+import logging
+
+log = logging.getLogger(__name__)
+
+
+def main() -> None:
+    logging.basicConfig(level=logging.INFO)
+    log.info("not implemented")

src/planemapper/models.py

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+from dataclasses import dataclass
+
+
+@dataclass
+class Aircraft:
+    icao: str
+    lat: float
+    lon: float
+    heading: float = 0.0
+    altitude_ft: int = 0
+    callsign: str = ""
+    category: str = ""
+    is_mlat: bool = False
+    is_stale: bool = False

src/planemapper/provision.py

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+import logging
+
+log = logging.getLogger(__name__)
+
+
+def main() -> None:
+    logging.basicConfig(level=logging.INFO)
+    log.info("not implemented")

src/planemapper/provisioning/__init__.py

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+class ProvisioningError(Exception):
+    pass

src/planemapper/provisioning/airspace.py

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+# stub

src/planemapper/provisioning/config.py

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+# stub

src/planemapper/provisioning/location.py

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+# stub

src/planemapper/provisioning/portal.py

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+# stub

src/planemapper/provisioning/tiles.py

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+# stub

src/planemapper/provisioning/wifi.py

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+# stub

src/planemapper/renderer/aircraft.py

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+# stub

src/planemapper/renderer/airspace.py

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+# stub

src/planemapper/renderer/basemap.py

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+# stub

src/planemapper/renderer/colours.py

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+# stub

src/planemapper/renderer/icons.py

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+# stub

src/planemapper/renderer/projection.py

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+# stub

src/planemapper/renderer/renderer.py

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+# stub