Landscape orientation, redesigned web UI, rotation on/off + minutes, weather by city name

- Panel is mounted sideways: render landscape (600x400), rotate to the
  panel's native portrait orientation right before writing to hardware.
- Web UI: card-based layout, dark mode, active nav highlighting, save
  confirmation toasts, error banners.
- Rotation: separate enabled/disabled toggle (off pins to the first screen
  in the list) and the interval is now in minutes instead of raw seconds.
  Migrates existing config.json from the old interval_seconds field.
- Weather: type a city name instead of hunting down coordinates, resolved
  via Open-Meteo's free geocoding API. Manual lat/long still available as
  a fallback.

scheduler.py

@@ -161,9 +161,14 @@ class Scheduler:
             screen_ids = list(self.screens.keys())
 
         now = time.time()
-        if now - self._rotation_switched_at >= rotation["interval_seconds"]:
-            self._rotation_index = (self._rotation_index + 1) % len(screen_ids)
-            self._rotation_switched_at = now
+        # With rotation disabled, just pin to whatever's currently selected --
+        # never auto-advance. (Manual "show this screen now" still works via
+        # request_switch(); it just won't stick past the next tick.)
+        if rotation.get("enabled", True):
+            interval_seconds = rotation["interval_minutes"] * 60
+            if now - self._rotation_switched_at >= interval_seconds:
+                self._rotation_index = (self._rotation_index + 1) % len(screen_ids)
+                self._rotation_switched_at = now
 
         screen_id = screen_ids[self._rotation_index % len(screen_ids)]
         cache = self._caches[screen_id]