feat(editor): properties-panel toggle + LabVIEW-style type colours

Two visible UX fixes:

1. Properties-panel toggle. Tap a step → opens. Tap the
   same step again → closes (deselect via toggle). Tap the
   canvas background → also closes. selectStep now returns
   to null when called with the already-selected id; the
   editor-controller test updated for the new semantics.

2. LabVIEW-style type colours on every port + wire.
   _typeAccent now picks vibrant brightness-aware hues per
   datatype:
     text   → magenta/pink (LabVIEW string)
     json   → amber/orange (cluster feel)
     bytes  → cyan/teal (raw binary)
     file   → green (file reference)
     number → yellow/amber
   Step-input dots, step-output dots, and outputs-endpoint
   dots all switch from the generic theme.primary to the
   field's declared type accent. Operators read the
   payload from the dot alone.

Editor tests still pass (20).

Signed-off-by: flemming-it <sf@flemming.it>

lib/src/widgets/flow_node.dart

@@ -101,11 +101,7 @@ class NodeGeometry {
   /// last port row overflows.
   static double heightFor(int inputCount, [int outputCount = 0]) {
     final rows = inputCount > outputCount ? inputCount : outputCount;
-    return headerHeight +
-        bodyTopPad +
-        rows * portRowHeight +
-        bodyBottomPad +
-        2;
+    return headerHeight + bodyTopPad + rows * portRowHeight + bodyBottomPad + 2;
   }
 
   /// Y offset (from the card's top edge) where the input