failure-panel uses a bare ease instead of a DESIGN.md easing token

[prekabreki]

Context

fetchforge/index.html:1047 is animation: fadeUp 0.3s ease both. DESIGN.md's Motion
section mandates easing tokens only (--ease-out for enter/exit, --ease-in-out for
on-screen movement, never bare ease-in). #48 converted the shutdown overlay's entry to
var(--ease-out) for exactly this reason; .failure-panel is the last bare ease left in
the file.

Cosmetic consistency, one line — filed so it does not sit as invisible drift.

Acceptance criteria

• .failure-panel uses var(--ease-out).
• grep -n "0.3s ease " fetchforge/index.html returns nothing.
• The panel still animates in on reveal, and still respects the reduced-motion block
  (it reuses fadeUp, which is redefined opacity-only there, so this should be free).

Files / where this lives

• fetchforge/index.html:1047 — .failure-panel
• DESIGN.md — Motion section, the rule being enforced

How to verify

• grep -n "0.3s ease " fetchforge/index.html — empty
• npx impeccable detect fetchforge/index.html — exit 0
• npm --prefix tests/frontend test — 25/25 still green

Constraints

• Do not change the duration or the keyframe, only the easing token.

Out of scope

• Any other motion tuning.

Notes

• Executor tier: cheap. Genuinely a one-line change.