[0.64.1] Animate budget disclosure chevron

[Finesssee]

Adds a short rotation transition to the budget disclosure chevron and disables it when reduced motion is preferred.

Validation:

• git diff --check passed.
• pnpm install --frozen-lockfile --offline and the frontend production bundle passed.
• The fresh Tauri debug build was stopped when free space crossed the 30 GiB guardrail (29.91 GiB). Native Windows CUA proof is pending; no stale binary or screenshot was used.
• Independent Luna source review found no issues.

[Finesssee]

Thermo-nuclear code-quality review

Verdict: PASS. No maintainability findings. Reviewed head a0de08cc0.

The change is a single transition on the existing ::before chevron, next to the rule it animates. The header is already display: flex, so the pseudo-element is blockified and the transform applies. The reduced-motion override sits in the same file as the rule it overrides.

Native proof is still required for this change: capture the chevron animating on a fresh Windows build, and with reduced motion turned on under Windows animation effects. That goes through the usual CUA evidence path.