fix(tui): avoid opentui-spinner color type conflicts

[gmnstr]

Issue for this PR

Closes #26119

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This fixes a package typecheck failure in packages/opencode/src/cli/cmd/tui/ui/spinner.ts caused by importing ColorGenerator through opentui-spinner.

The problem is that the repo uses @opentui/core@0.2.2, while opentui-spinner@0.0.6 is typed against @opentui/core@^0.1.49. That causes Bun to install two different @opentui/core type graphs, and the branded ColorInput / RGBA types stop matching.

This PR replaces the imported ColorGenerator type with an equivalent local structural alias in spinner.ts.

Why this works:

• it avoids pulling the conflicting nested @opentui/core types through opentui-spinner
• runtime behavior does not change because this is type-only wiring
• bun typecheck succeeds again in packages/opencode

How did you verify your code works?

From packages/opencode:

• bun typecheck

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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