feat: dual-board architecture — ESP8266 camera bridge + ESP32 MQTT bridge

Complete rewrite of firmware into two dedicated boards per camera node:

ESP8266 (Camera Bridge):
- Connects ONLY to GoPro AP — polls status, sends over UART
- Zero network switching, zero MQTT
- HTTP GET /bacpac/SH for status, start/stop
- JSON-per-line UART protocol to ESP32

ESP32 (MQTT Bridge):
- Connects ONLY to travel router — MQTT to Pi hub
- Reads status from ESP8266 over UART2 (RX16/TX17)
- Auto-registration, heartbeat, command forwarding
- Zero camera communication

UART Protocol: JSON-per-line at 115200 8N1
  ESP8266→ESP32: status/ack/pong/error
  ESP32→ESP8266: cmd (start_recording/stop_recording/ping)

Hardware updates:
- BOM now includes both boards (~4/node)
- 3D case has stacked dual-board compartment
- UART wire channel between board recesses
- Shared 3.3V power rail for both boards

hardware/case/remoterig-case.scad

@@ -15,12 +15,19 @@ gopro_depth  = 30;   // mm — body depth (front to back)
 gopro_lens_dia = 28; // mm — lens protrusion diameter
 gopro_lens_offset = 18; // mm — lens center from top
 
-// ── ESP32 D1 Mini ──
-esp_width  = 34.2;
-esp_height = 25.6;
-esp_thick  = 5;       // board + components
-usb_cutout_w = 10;
-usb_cutout_h = 5;
+// ── ESP8266 D1 Mini + ESP32 Dev Board (stacked) ──
+esp8266_width  = 34.2;
+esp8266_height = 25.6;
+esp8266_thick  = 5;       // board + components
+
+esp32_width  = 52;        // ESP32 Dev Board is larger
+esp32_height = 28;
+esp32_thick  = 5;
+
+// Combined stack
+board_width  = max(esp8266_width, esp32_width);
+board_height = max(esp8266_height, esp32_height);
+board_thick  = esp8266_thick + esp32_thick + 3; // 3mm gap between boards
 
 // ── LiPo Battery (1000mAh typical) ──
 lipo_width  = 35;
@@ -30,7 +37,7 @@ lipo_thick  = 8;
 // ── Case parameters ──
 wall = 2.0;           // case wall thickness
 tolerance = 0.3;      // print tolerance for friction fit
-compartment_height = max(esp_thick, lipo_thick) + 3; // internal compartment height
+compartment_height = board_thick + 5; // internal compartment height for stacked boards
 
 // ── Cable channels ──
 cable_dia = 4;        // USB cable diameter
@@ -103,13 +110,13 @@ module gopro_sleeve() {
 }
 
 // ══════════════════════════════════════════════════════════════
-// Electronics Compartment — holds ESP32 + routes cables
+// Electronics Compartment — holds ESP8266 + ESP32 stacked
 // ══════════════════════════════════════════════════════════════
 
 module electronics_compartment() {
-    comp_w = max(esp_width, esp_height) + wall*2 + 10;
+    comp_w = board_width + wall*2 + 8;
     comp_h = compartment_height + wall*2;
-    comp_d = gopro_depth + wall*2;
+    comp_d = board_height + wall*2 + 8;
     
     difference() {
         union() {
@@ -128,14 +135,22 @@ module electronics_compartment() {
         translate([0, 0, wall])
         rounded_cube(comp_w - wall*2, comp_d - wall*2, comp_h - wall, 2);
         
-        // ESP32 board recess
+        // Bottom board (ESP32 — larger) recess
         translate([0, 5, wall + 1])
-        cube([esp_width + tolerance, esp_height + tolerance, esp_thick + 1], center=true);
+        cube([esp32_width + tolerance, esp32_height + tolerance, esp32_thick + 1], center=true);
         
-        // USB cable entry (side hole)
+        // Top board (ESP8266 — smaller) recess  
+        translate([0, 5, wall + esp32_thick + 4])
+        cube([esp8266_width + tolerance, esp8266_height + tolerance, esp8266_thick + 1], center=true);
+        
+        // UART wire channel (between boards)
+        translate([comp_w/2, 0, wall + esp32_thick + 1])
+        cube([wall*3, 6, 3], center=true);
+        
+        // USB cable entry (power to boards)
         translate([comp_w/2, 15, comp_h/2])
         rotate([0, 90, 0])
-        cylinder(d=usb_cutout_w, h=wall*3, center=true);
+        cylinder(d=6, h=wall*3, center=true);
         
         // USB cable exit (to GoPro)
         translate([comp_w/2, -15, comp_h/2])
@@ -150,9 +165,11 @@ module electronics_compartment() {
             }
         }
         
-        // LED window (thin wall for ESP32 LED visibility)
+        // LED windows (thin walls for ESP LEDs)
         translate([0, 0, wall])
         cube([5, 5, wall], center=true);
+        translate([0, 0, wall + esp32_thick + 4])
+        cube([5, 5, wall], center=true);
     }
 }