Improve on-demand capture color startup

[yvette-carlisle]

Summary

• release screen recording resources outside active capture while keeping cold activation responsive
• reduce cold live color sampling latency by retaining/preparing the live sampler worker and tightening stream/sampler ownership
• smooth cold HUD color reveal with a one-shot hex tumbler animation that does not replay during pointer movement sample gaps

Validation

• cargo make fmt-swift-check
• cargo make build-swift-strict
• git diff --check
• ./scripts/build_and_run.sh run