Use admission time for streaming accent decay

[pat-oai]

Summary

• Uses both admission time and scheduled reveal time when deciding streaming accent strength.
• Caps each accent overlay duration at the shared decay window so delayed text does not outlive the opening accent treatment.
• Keeps existing animation count bounded by skipping excess accent overlays instead of evicting active ones.

Why

Streaming text can reveal adjacent markdown blocks at slightly different times. If each overlay only uses its local reveal timing, already-revealed text can lose the accent while the next block is still starting, making the transition look inconsistent. This keeps the treatment tied to the shared opening window while preserving per-segment reveal timing.

Testing

• JAVA_HOME=/opt/homebrew/Cellar/openjdk@21/21.0.10/libexec/openjdk.jdk/Contents/Home ANDROID_HOME=/Users/pat/Library/Android/sdk ./gradlew :richtext-ui:check