docs: precise SNEK callback config for JSON POST body

- Step-by-step field-by-field callback config table
- Common pitfall documented: don't paste JSON body in "Line pattern"
- Exact JSON body template format (spaces around colons required)
- Companion dashboard deployment steps

Backend also cleaned up: unified query-string / JSON body parsing
via a single _num() helper instead of nested try/except blocks.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dashboard/app.py

@@ -63,19 +63,24 @@ def index():
     return send_from_directory("static", "index.html")
 
 
-@app.route("/webhook", methods=["POST"])
+def _num(x, cast=float):
+    try:
+        return cast(x)
+    except (TypeError, ValueError):
+        return None
+
+
+@app.route("/webhook", methods=["POST", "GET"])
 def webhook():
-    """
-    SNEK callback endpoint.
-    SNEK sends JSON with: device, time, data, rssi, snr, seqNumber, etc.
-    """
-    body = request.get_json(force=True, silent=True) or {}
-    device = (body.get("device") or "").lower()
-    raw = (body.get("data") or "").lower()
-    ts = float(body.get("time") or time.time())
-    rssi = body.get("rssi")
-    snr = body.get("snr")
-    seq_number = body.get("seqNumber")
+    """SNEK callback endpoint. Accepts JSON body OR query string / form params."""
+    src = request.get_json(force=True, silent=True) or request.values
+
+    device = (src.get("device") or "").lower()
+    raw = (src.get("data") or "").lower()
+    ts = _num(src.get("time")) or time.time()
+    rssi = _num(src.get("rssi"))
+    snr = _num(src.get("snr"))
+    seq_number = _num(src.get("seqNumber") or src.get("seqnumber"), int)
 
     if not device or not raw:
         return jsonify({"error": "missing device or data"}), 400