Migrate Stratos color tokens from RGB/hex to OKLCH (Tailwind v4)

[nabramovitz]

Summary

Move the Stratos color token values from RGB/hex to OKLCH. Tailwind v4 (^4.3.1, already in use) defines its default palette in OKLCH, so this aligns Stratos with Tailwind's own direction rather than fighting it.

Why

• Perceptually-uniform light/dark math. Dark mode done right is perceptual lightness inversion, not per-channel RGB inversion (255-r produces garish results). In OKLCH that's simply L → 1−L (keep chroma/hue), plus optional C×0.5 and a small hue shift for an atmospheric dark palette. This makes paired light/dark token generation a known, small transform.
• Consistency with Tailwind v4, whose palette is already OKLCH.
• Unblocks the stb theming tool's OKLCH picker, which currently ships its oklch format option disabled ("oklch (planned)") because there was no rgb→oklch conversion on the token path.

Scope

• Convert @theme token definitions (and any remaining hardcoded hex) to oklch(...) values.
• The conversion itself is solved — OKLCH↔hex round-trips already exist; RGB/hex is just the entry/exit boundary.
• Follow-on to Normalize remaining hard-coded / light-only colors to semantic theme tokens (light/dark) #5494 (semantic-token normalization): Normalize remaining hard-coded / light-only colors to semantic theme tokens (light/dark) #5494 made colors semantic; this makes the values perceptual.
• Re-enable the stb OKLCH format option once the token path carries OKLCH.

Notes

• hex→OKLCH→hex is mildly lossy at gamut edges — acceptable here (we're standardizing token values, and generating dark variants, not pixel-preserving a single color).
• Light/dark derivation math reference: standard OKLCH invertLightness(l,c,h) = {l: 1−l, c, h} + chroma/hue adjustment.

Related: #5494 (semantic theme tokens), FWT-866/FWT-868 (token classes / dark-mode templates), theming/branding (stb) workstream.