Add a 3D-printed photo frame insert for the panel and D1 mini

OpenSCAD truss insert that holds the EL512.256-H and a Wemos D1 mini
ESP32 in a 250 x 200 x 30 mm photo frame. The D1 mini snap-tab lips
print without supports: a 45 degree chamfer bridges the gap to the
pocket, only the catch is a short flat overhang, and the tip is blunt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -99,6 +99,7 @@ home_assistant/packages/  el512_panel.yaml: helper sensors for the ESPHome pages
 tools/                  import_still_alive.py, konosuba_sprites.py, steins_sprites.py,
                         trek_sprites.py, yourname_sprites.py, render_pages.py
                         (+ render/: PC renderer)
+enclosure/              el512_frame.scad: 3D-printed insert for a 250x200x30 photo frame
 test/                   unit tests (placeholder)
 docs/                   datasheet and notes
 ```