fix: harden shell scripts with error handling and null guards

- dashboard.sh: Add // [] jq null guard on .data.array.disks[] (L176-177)
  Resolves review thread PRRT_kwDOO6Hdxs5uvO21

- dashboard.sh: Default NAME to server key when env var unset (L221)
  Resolves review thread PRRT_kwDOO6Hdxs5uvO22

- unraid-query.sh: Check curl exit code, empty response, and JSON validity
  before piping to jq (L112-129)
  Resolves review thread PRRT_kwDOO6Hdxs5uvO24

- disk-health.sh: Guard against missing query script and invalid responses
  Resolves review thread PRRT_kwDOO6Hdxs5uvKrh

skills/unraid/scripts/unraid-query.sh

@@ -112,7 +112,21 @@ CURL_FLAGS=("-sL" "-X" "POST")
 RESPONSE=$(curl "${CURL_FLAGS[@]}" "$URL" \
     -H "Content-Type: application/json" \
     -H "x-api-key: $API_KEY" \
-    -d "$PAYLOAD")
+    -d "$PAYLOAD") || {
+    echo "Error: curl request failed (exit code $?). Check URL and network connectivity." >&2
+    exit 1
+}
+
+if [[ -z "$RESPONSE" ]]; then
+    echo "Error: Empty response from server." >&2
+    exit 1
+fi
+
+if ! echo "$RESPONSE" | jq -e . > /dev/null 2>&1; then
+    echo "Error: Server returned invalid JSON. Response:" >&2
+    echo "$RESPONSE" | head -c 500 >&2
+    exit 1
+fi
 
 # Check for errors
 if echo "$RESPONSE" | jq -e '.errors' > /dev/null 2>&1; then