install.sh: update credentials template to current format

Switch from flat username/password keys to nested credentials block
and add interval_s, host, port, log_dir with their defaults.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

install.sh

@@ -51,10 +51,16 @@ chmod 700 "$CREDS_DIR"
 if [[ ! -f "$CREDS_FILE" ]]; then
     cat > "$CREDS_FILE" <<'EOF'
 {
-  "username": "me@example.com",
-  "password": "secret",
-  "vin":      "",
-  "domains":  ["charging", "measurements", "readiness"]
+  "credentials": {
+    "username": "me@example.com",
+    "password": "secret"
+  },
+  "vin":        "",
+  "domains":    ["charging", "measurements", "readiness"],
+  "interval_s": 300,
+  "host":       "0.0.0.0",
+  "port":       9999,
+  "log_dir":    "./logs"
 }
 EOF
     chmod 600 "$CREDS_FILE"
@@ -110,7 +116,7 @@ echo "━━━━━━━━━━━━━━━━━━━━━━━━
 echo " Installation complete."
 echo ""
 echo " Next steps:"
-echo "   1. Edit credentials:"
+echo "   1. Edit credentials (username, password, vin, interval_s, …):"
 echo "        \$EDITOR $CREDS_FILE"
 echo ""
 echo "   2. Start the service:"