fix(registry): connector geometry, family accent, and demo legibility

Found by stepping through motion contact sheets rather than single frames.

- hw-pipeline: arrowheads were two asymmetric barbs (l -30 -14 / l -26 18)
  fixed to horizontal, so they detached from a curve that arrives on a
  descending tangent. Barbs now derive from the quadratic's end tangent
  (end - control) with symmetric length and spread.
- hw-pipeline, hw-scribble-transition, hw-callout-circle: the family carried
  two accents — #ffb020 in hw-frame/hw-title/hw-underline and #6d6dff here.
  Unified on the warm marker accent; the blue read as a default UI colour.
- hw-callout-circle: the scribble hatch rendered as stacked bars over the
  labelled subject. More rows so the zigzag reads as a scribble, lighter
  weight and alpha so it sits behind the label.
- yt-camera-move: the stage grid was too faint to reveal the move, so the
  preview of a camera-move component looked static. Stronger grid; zoom,
  slide and tilt now read.

Demos resynced from source — demo.html is a plate-swapped copy, so a source
fix does not reach the catalog preview until it is regenerated.

registry/blocks/hw-scribble-transition/hw-scribble-transition.html

@@ -16,7 +16,9 @@
         overflow: hidden;
       }
       #hw-st-root {
-        --hw-accent: #6d6dff;
+        /* Warm marker accent, consistent with the rest of the hw family.
+           Override per use via CONFIG.color. */
+        --hw-accent: #ffb020;
 
         position: relative;
         width: 1920px;
@@ -75,7 +77,7 @@
            coverage at the midpoint (the host hard-cuts beneath, ~0.9-1.4s
            local), then everything clears. Place spanning the host's cut. */
         var CONFIG = {
-          color: null, // css color; null = --hw-accent purple
+          color: null, // css color; null = --hw-accent (warm marker)
           bands: 7, // horizontal scribble bands
           strokeScale: 1.0,
           seed: 17,