refinements proposal for #342

[marcalexiei]

• Related to fix warnings #342

fix(top-languages): default color when a language has no color

GitHub's Language.color is nullable, so a language can reach the card with color: null.

The compact, pie, donut, and donut-vertical layouts validated the raw color and threw on null,
turning a normal request into a "Something went wrong" error card (previously such languages rendered gray).

refactor(core): restructure color validation

Cleans up common/color.ts (no behavior change for valid inputs):

• Split the isValidHexColor(x, numberSignPrefix) into isBareHexColor / isPrefixedHexColor.
• Moved the hex regex to a module constant (was rebuilt on every call in render loops).
• Gradient angle now validated with Number.isFinite (rejects Infinity)
• Reworked color.test.ts for the two predicates + non-finite-angle cases.

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[martin-mfg]

The compact, pie, donut, and donut-vertical layouts validated the raw color and threw on null,
turning a normal request into a "Something went wrong" error card (previously such languages rendered gray).

Good catch!