feat: Add new Geometry Nodes groups for image relief and shadeless shader

- Implemented the "O Image Relief Plane" Geometry Nodes group to create a fixed-base image relief using depth images and various parameters.
- Created the "O Shadeless" shader node group to display color without scene lighting while preserving shadows and reflections.
- Introduced a preview feature for node groups, allowing for interactive visualization of node arrangements in an HTML format.
- Added a template HTML file for rendering node previews with customizable views and controls.

tools/nodes/arrangement/connections.py

@@ -0,0 +1,39 @@
+"""Socket endpoints and conservative curve footprints for placement and preview."""
+
+from .flow import socket_links
+
+
+def socket_position(socket, positions, sizes):
+    node = socket.node
+    x, y = positions[node]
+    if node.bl_idname == "NodeReroute":
+        return x + 8, y - 8
+    return x + (sizes[node].width if socket.is_output else 0), y - sizes[node].sockets[socket]
+
+
+def link_endpoints(link, positions, sizes):
+    start = socket_position(link.from_socket, positions, sizes)
+    x, y = socket_position(link.to_socket, positions, sizes)
+    if link.to_socket.is_multi_input:
+        siblings = socket_links(link.to_socket)
+        y -= (siblings.index(link) - (len(siblings) - 1) / 2) * 8
+    return start, (x, y)
+
+
+def curve_footprint(start, end):
+    """Reserve eight convex hulls covering a horizontal-tangent Bezier curve."""
+    x1, y1 = start
+    x2, y2 = end
+    bend = max(40, abs(x2 - x1) * 0.42)
+    curves = [(start, (x1 + bend, y1), (x2 - bend, y2), end)]
+    for _ in range(3):
+        divided = []
+        for points in curves:
+            rows = [points]
+            for _ in range(3):
+                rows.append([((a[0] + b[0]) / 2, (a[1] + b[1]) / 2)
+                             for a, b in zip(rows[-1], rows[-1][1:])])
+            divided.extend((tuple(row[0] for row in rows), tuple(row[-1] for row in reversed(rows))))
+        curves = divided
+    return [(min(x for x, _ in curve), max(x for x, _ in curve),
+             max(y for _, y in curve), min(y for _, y in curve)) for curve in curves]