List derived percentage fields

List all available derived percentage fields.

Derived fields are computed at query time from raw census data. Use them with ?fields=derived.pct_indigenous on the demographics endpoint.

63 static fields, always available, no extra params needed. Covers:

• Population (G01): indigenous, born overseas/australia, english/other language, citizen, children, working age, seniors, education attendance, school completion
• Age brackets (G01): 11 fields for each G01 age bracket (0-4 through 85+)
• Motor vehicles (G34): no car, 1/2/3+ cars
• Dwelling structure (G42): separate house, semi-detached, flat/apartment, other
• Labour force (G43): unemployed, full/part-time, in/not in labour force
• Qualifications (G43): postgrad, bachelor, grad diploma, adv diploma, cert III/IV, I/II
• Migration (G43): moved 1yr/5yr ago, same address
• Household income (G33): negative/nil, under $650, $1k-2k, $2k+/week
• Rent (G40): under $200, $200-449, $450+/week
• Mortgage (G38): under $600, $600-999, $1000+/month
• Household composition (G35): lone person, large (5+), family household