feat(view): add 3D pier viewer and P1 sample page

- three.js scene in the pier frame (pivot at first column centre)
- coping as extruded elevation outline; columns, footings, piles, blinding, bearing blocks and pads
- four view presets, per-part visibility toggles
- workbook load (sample or file), result table, issue list and undetermined defaults
- frame orientation test and bounding-box test

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

src/vite-env.d.ts

@@ -0,0 +1 @@
+/// <reference types="vite/client" />