feat: live ESP32 CSI pipeline + auto-connect WebSocket

- Add auto-connect to local sensing server WebSocket (ws://localhost:8765)
- Demo shows "Live ESP32" when connected to real CSI data
- Add build_firmware.ps1 for native Windows ESP-IDF builds (no Docker)
- Add read_serial.ps1 for ESP32 serial monitor

Pipeline: ESP32 → UDP:5005 → sensing-server → WS:8765 → browser demo

Co-Authored-By: claude-flow <ruv@ruv.net>

firmware/esp32-csi-node/read_serial.ps1

@@ -0,0 +1,14 @@
+$p = New-Object System.IO.Ports.SerialPort('COM7', 115200)
+$p.ReadTimeout = 5000
+$p.Open()
+Start-Sleep -Milliseconds 200
+
+for ($i = 0; $i -lt 60; $i++) {
+    try {
+        $line = $p.ReadLine()
+        Write-Host $line
+    } catch {
+        break
+    }
+}
+$p.Close()