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.

screens/base.py

@@ -0,0 +1,28 @@
+"""Base interface every screen implements."""
+
+from abc import ABC, abstractmethod
+from typing import Any
+
+from PIL import Image
+
+
+class Screen(ABC):
+    id: str
+    display_name: str
+    poll_interval: int = 60  # seconds between check() calls
+
+    @abstractmethod
+    def check(self, settings: dict) -> Any:
+        """Cheap call (ideally a single small request) that returns whatever
+        state this screen needs to render. Returning None means "nothing to
+        show" (only meaningful for preemptive screens like Navidrome)."""
+
+    @abstractmethod
+    def render(self, state: Any, settings: dict, resolution: tuple[int, int]) -> Image.Image:
+        """Full draw. Only called when this screen is actually about to be
+        shown, so it's fine for this to be more expensive than check()."""
+
+    def default_settings(self) -> dict:
+        """Settings this screen needs, with defaults, merged under config.json's
+        settings[self.id] on first run."""
+        return {}