fix(cli): disable Freebuff chat logo sheen

[c8dhjp4tyv-bit]

Recreated on the rewritten main after #1102 was auto-closed during repository maintenance. This carries the same reviewed change set on the new history.

Summary

• disable the animated chat-header logo sheen in Freebuff builds
• keep the existing animation for standard Codebuff builds
• add focused regression coverage for both product paths

Fixes #1035

Validation

Prior validation before the history rewrite:

• focused animation tests: 3 passed
• related queue tests: 4 passed
• full CLI suite: 2,367 passed, 9 skipped; existing checkout/environment failures remain (34 failed tests and 32 harness errors)
• CLI typecheck: existing missing tar and react-dom/server declarations; no errors from changed files
• Prettier check for changed files: passed
• git diff --check: passed

[codebuff-team]

Clean, minimal change. IS_FREEBUFF was already imported and used in chat-header.tsx, so gating the sheen animation on it follows existing convention rather than introducing new branching logic. The extraction into shouldAnimateChatHeader as a pure function is a nice touch — easy to unit test in isolation (chat-header-animation.test.ts), and the three cases (Freebuff+enabled, Codebuff+enabled, disabled for both) cover the meaningful branches.

A couple of minor points a maintainer will likely want addressed before porting:

• No visual/manual confirmation mentioned beyond the unit tests — since this is a rendering/animation change, it'd help to note that the static logo still renders correctly in Freebuff builds (colors, block layout unaffected), not just that the boolean flips.
• The docstring in chat-header-animation.ts states a specific rationale ("can make the focused input appear to flicker") tied to issue Can the FREEBUFF flashing effect displayed by CLI be turned off? It is currently causing the input method to flicker #1035 — worth double-checking that's still the accepted justification post-rewrite, since the PR references a rewritten history and a prior closed PR (fix(cli): disable Freebuff chat logo sheen #1102).

Otherwise this is exactly the kind of small, targeted, testable fix that's easy to port by hand. Good work.

[c8dhjp4tyv-bit]

Addressed both follow-ups. The helper docstring is now behavioral rather than asserting an unverified post-rewrite flicker cause. I also rechecked the rendering diff: the only chat-header.tsx behavior change is the enabled argument passed to the sheen hook; logoColor, accentColor, blockColor, and the header layout/rendering path are untouched. The focused animation tests pass 3/3, covering Freebuff static, Codebuff animated, and globally-disabled cases.