end-to-end working: ESP32 connects to server, renders widgets

boot logo (procedural hexagon + K), WiFi (WPA auto-detect with retries),
TCP client connects and receives ScreenUpdate/DataUpdate messages,
display renders widget data. Makefile with esp-flash/server/desktop targets.

known issues: boot logo not cleared, text overlaps, occasional reconnect

crates/client-esp32/src/config.rs

@@ -11,6 +11,10 @@ pub const SCREEN: BoundingBox = BoundingBox {
     height: SCREEN_HEIGHT,
 };
 
+// Physical panel dimensions (before rotation)
+pub const PANEL_WIDTH: u16 = 240;
+pub const PANEL_HEIGHT: u16 = 320;
+
 pub const SPI_BAUDRATE: Hertz = Hertz(26_000_000);
 pub const SPI_BUFFER_SIZE: usize = 512;