fix(theme): align color tone role mappings

[artiphishle]

Summary

Closes #18.

Audits and tightens Surface color-tone role palette mappings against the app-facing background/foreground lane direction without adding a ZORA dependency.

Behavior changes:

• fluorescent now uses obsidian background/surface roles and fluorescent action roles.
• pastel keeps pastel background/surface roles but moves foreground/action roles to jewel-like roles.
• earth keeps earth background/surface roles but moves primary/secondary action roles to mineral-like roles.

Tests added for semantic behavior instead of exact snapshots:

• obsidian/fluorescent dark surfaces remain low-lightness
• fluorescent action colors remain higher chroma than neutral actions
• pastel backgrounds remain lower chroma than foreground/action colors
• earth action chroma aligns with mineral-like chroma
• generated palettes still emit required semantic roles for every ColorTone

Scope boundaries

No ZORA dependency, no ColorTone rename, no new dependencies, and no full engine rewrite.

Verification

Not run locally from this environment. GitHub CI should run on the PR.