[a11y] reduce-motion follow-ups: bot speech bounce, hologram boot shimmer

[nickmeinhold]

Motivation

PR #440 deliberately scoped reduce-motion conservatively. Two animations were flagged borderline and deferred:

• Bot bubble speech bounce — the bot bubble bounces slightly when speaking. Borderline: it's informational (signals "bot is speaking") but the same info is in the audio track. Reduce-motion users may prefer the visual signal even off; or may want it suppressed and rely on audio.
• Hologram boot shimmer — purely informational animation when a hologram avatar first appears. Probably safe to suppress.

Scope

• Decide which gate(s) to apply
• Implementation is a one-line conditional in the relevant component, same pattern as PR feat(bubbles): reduce-motion user preference #440

Status

Not blocked. Trivial scope. Worth bundling with one of the other a11y PRs as a hygiene pass rather than a standalone PR.

Related

• PR feat(bubbles): reduce-motion user preference #440 (reduce-motion) — see PR body "Deferred follow-ups"