Initial commit: Paperwall, a standalone e-ink dashboard

Navidrome now-playing, clock, and weather for a Waveshare epd4in0e panel,
with a local web UI and install/uninstall scripts for the Pi.

display/__init__.py

@@ -0,0 +1,28 @@
+"""Display driver interface.
+
+A driver only needs to do three things: get ready, put an image on the panel,
+and go to sleep to save power. `EPD4in0eDisplay` talks to the real Waveshare
+hardware; `MockDisplay` is a drop-in stand-in for developing off the Pi.
+"""
+
+from abc import ABC, abstractmethod
+
+from PIL import Image
+
+
+class Display(ABC):
+    resolution: tuple[int, int]
+
+    @abstractmethod
+    def init(self) -> None:
+        """Prepare the panel for writing (called once at startup, and again
+        after every sleep since most EPDs need re-initializing)."""
+
+    @abstractmethod
+    def show(self, image: Image.Image) -> None:
+        """Push a full-resolution image to the panel. This is always a full
+        refresh on this hardware -- there is no partial-refresh path."""
+
+    @abstractmethod
+    def sleep(self) -> None:
+        """Put the panel into low-power mode between updates."""