Add specs, high-speed tag, and 1kg packages for ELEGOO Rapid PETG line

[crzykidd]

Fills out the ELEGOO Rapid PETG line — all 12 colors already existed (color + photo)
but had no specs or packages. This adds print specifications, the high_speed tag,
and a 1kg package per color.

Materials (12, enriched)

Black, White, Red, Blue, Green, Yellow, Grey, Orange, Brown, Transparent, Beige, Space Grey

• Properties from the official ELEGOO Rapid PETG spec sheet:
  • Nozzle 240–270 °C, bed 65–75 °C, drying 60 °C / 8 h, density 1.29 g/cm³, nozzle ≥0.2 mm
  • Chamber omitted (enclosure "Not Required").
• Tag high_speed added (Rapid line, <600 mm/s, "high-speed printing" key feature).
• Spec-sheet values with no schema field (melt index, melting temp, Vicat, HDT,
  tensile/elongation/bending/impact, print speed, humidity) are omitted.
• Colors and photos unchanged.

Packages (12, new)

• elegoo-rapid-petg-{color}-1kg, 1000 g, 1.75 mm, on elegoo-cardboard-spool-1kg
• brand_specific_id = ELEGOO SKU (SPUS-EL-PTG-1xx); variant product URL on the package
• GTIN-less for now (no barcodes on the listing) — backfillable later

Product: https://us.elegoo.com/products/rapid-petg-filament-1-75mm-colored-1kg
make validate passes; README/manifest untouched.