Add procedural palette generation

[kosmickroma]

What

Generate color palettes algorithmically at runtime instead of only using the hand-crafted ones in PALETTES.

Why

117 palettes is great but procedural generation means infinite variety — every era could potentially get its own
unique palette that has never existed before.

Ideas to explore

• Random hue rotation with locked saturation/brightness relationships
• Complementary, triadic, or analogous color theory schemes
• Perlin noise driven palette that slowly shifts hue over time
• Palette seeded from the era's seed number so it's fully reproducible

Where to look

• nca/params.py — PALETTES dict and sample_params() where palettes get picked
• display/windows.py — apply_palette_heat() where palettes get applied
• Generated palettes should return the same format as existing ones: a list of 4 RGB tuples

Notes

• Should work alongside existing hand-crafted palettes, not replace them
• Reproducibility matters — same seed should always produce same palette