Add the 19" rack adapter CAD package and the v2 plan

cad/ holds the left/right side adapters that mount the GeeekPi 9" 3U
touchscreen (a 10" mini-rack part) into a standard 19" rack: OpenSCAD
source, STLs, Anycubic Mega Pro gcode, and SendCutSend DXFs for the
sheet-metal version. Geometry is physically tested in a 19" rack.

notes/PLAN-v2.md is the reviewed plan for the Rust rewrite.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

cad/geeekpi_rack_adapter_release_v1/validation_release-v1.json

@@ -0,0 +1,48 @@
+{
+  "LEFT": {
+    "non_keystone_geometry_unchanged": true,
+    "keystones": [
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 65.0,
+        "center_y": 31.5
+      },
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 65.0,
+        "center_y": 66.0
+      },
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 65.0,
+        "center_y": 100.5
+      }
+    ]
+  },
+  "RIGHT": {
+    "non_keystone_geometry_unchanged": true,
+    "keystones": [
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 67.3,
+        "center_y": 31.5
+      },
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 67.3,
+        "center_y": 66.0
+      },
+      {
+        "width": 16.0,
+        "height": 22.0,
+        "center_x": 67.3,
+        "center_y": 100.5
+      }
+    ]
+  }
+}