Add Aluwdoors configurator reference assets

Downloaded 21 assets from configurator.aluwdoors.com:

Glass Textures (6):
- blank, brons, grijs (clear glass variations)
- mat-blank, mat-brons, mat-zwart (frosted glass)

Metal Textures (6):
- antraciet, beige, brons, goud, zwart, ral-keuze
- High-res JPGs (175-208KB) for realistic material rendering

Handle Types SVG (5):
- beugelgreep (bracket handle)
- geen (no handle)
- hoekgreep (corner handle)
- maangreep (moon handle)
- ovaalgreep (oval handle)

Divider Types SVG (2):
- platte-roede (flat divider)
- t-roede (T-profile divider)

Door Direction SVG (2):
- DIN-links (left swing)
- DIN-rechts (right swing)

Created scripts/download-assets.sh for reproducible downloads

Location: public/textures/aluwdoors/
Total size: ~2.8MB

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

public/textures/aluwdoors/aluwdoors-configurator-draairichting-DIN-links.svg

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