Refine hero-vs-warms categorical palette

Problem

The chart-library palette work has now stabilized around hero-6, a "hero blue versus neutrals" six-color palette. That resolves the primary hero need for M1, but it leaves a promising alternate concept unfinished: hero-vs-warms.

The team wants to preserve the current hero-vs-warms draft and the reasoning behind it without forcing it into M1 before it is ready. The remaining work is to decide whether it can become a second hero-style palette after further support-band, ordering, and separability refinement.

Context

• Stable hero palette now lives in docs/docs/guides/hero-palette.md as hero-6.
• hero-vs-warms is a different architecture from hero-6: it uses one strong blue hero against a set of warm support colors.
• During planning, a key correction was that hero palettes should not simply reuse the default ten-color palette. They need their own perceptual bands.
• For hero-vs-warms, the intended architecture is: primary contrast by hue, secondary contrast by lightness.
• The draft support colors should remain lighter than the hero blue and should avoid collapsing into one muddy warm band.
• Current preserved draft: 1. #2768a3 2. #c9954f 3. #d98d67 4. #c89d7d 5. #c8ab84 6. #b8995f

Possible Solutions

• Keep the current draft exactly as-is. Simple preservation, but it may still contain support-band compression or ordering weaknesses.
• Collapse the draft back into the default palette logic. Easier to maintain, but it loses the whole point of a hero-vs-warms architecture.
• Recommended: preserve the current draft as the baseline, then refine it as a distinct six-color hero-style palette with explicit support-band rules, lightness targets, and adjacency testing.

Plan

• Preserve the current draft in durable docs and in this task.
• Re-run warm-support separability checks using the local palette checker and real chart-use judgment.
• Decide whether the support colors need a stricter lightness band or ordering change.
• If the palette becomes coherent enough, document it as a second hero-style palette; otherwise, keep it as a research draft.

Implementation Progress

• 2026-03-24: task created to hold the downstream refinement thread after hero-6 stabilized as the primary hero palette.
• 2026-03-24: preserved current draft palette in task context and in docs/docs/guides/hero-palette.md.
• 2026-03-25: reviewed the current roadmap position and decided this does not need to remain an active task. The important job was preserving the draft and its reasoning, which is already handled in durable palette docs. No active follow-on milestone work is planned unless the palette becomes strategically relevant again.

QA Exploration

• [x] QA exploration completed (or N/A for non-UI tasks)
• N/A for planning-only palette refinement at this stage.

Review Feedback

• [x] Review cleared
• Closed as documentation preservation and roadmap cleanup; no additional code review was needed for the archival decision.