feat(editor): tab-aware action strip + simpler tap handling

Reposition the per-tab action buttons under the TabBar so the
operator's eye flows TabBar → context buttons → canvas. Graph
keeps Add-Step + Save + Run, Text trims to Save + Run, Run
hides them entirely (the Run tab has its own start button).

Drop the outer wrapping GestureDetector that competed with the
inner Positioned.fill detector inside the canvas Stack — two
TapGestureRecognizers in the same arena meant the inner one
sometimes lost edge-tap and background-tap.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/src/widgets/flow_canvas.dart

@@ -429,26 +429,6 @@ class _FlowCanvasState extends State<FlowCanvas>
           : BoxDecoration(color: theme.colorScheme.surface),
       child: Stack(
         children: [
-          // Outer-most tap layer — catches clicks on the
-          // dark area OUTSIDE the canvas grid (when the
-          // operator has panned / zoomed so the grid
-          // doesn't fill the viewport). Translucent so
-          // InteractiveViewer below still handles pan +
-          // zoom; the gesture arena gives the tap to
-          // whichever child claims it first, and on
-          // canvas-empty pointers nobody else does.
-          Positioned.fill(
-            child: GestureDetector(
-              behavior: HitTestBehavior.translucent,
-              onTap: () {
-                // Deselect both step + edge so the
-                // properties panel closes when the operator
-                // clicks the empty backdrop.
-                widget.controller.selectStep(null);
-                widget.controller.selectEdge(null);
-              },
-            ),
-          ),
           InteractiveViewer(
             transformationController: _transform,
             constrained: false,