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>

pubspec.yaml

@@ -1,6 +1,6 @@
 name: fai_studio_flow_editor
 description: Swappable inline YAML editor for F∆I Studio flows.
-version: 0.11.0
+version: 0.12.0
 publish_to: 'none'
 repository: https://git.flemming.ai/fai/studio-flow-editor