Add PoE variant with W5500 Ethernet and 802.3af power

- W5500 SPI Ethernet controller for wired connectivity
- Silvertel Ag9905MT PoE PD module (48V to 5V)
- RJ45 connector with integrated magnetics
- Higher camera resolution (1024x768 vs 800x600) using wired bandwidth
- WiFi fallback if Ethernet disconnected
- Separate BOM, pin mapping, ESPHome config
- 3D-printable enclosure (50x40mm, larger for RJ45)

poe-variant/lid_only_poe.scad

@@ -0,0 +1,2 @@
+use <enclosure-poe.scad>;
+lid();