feat: expose runtime previews and restore transient labels

[Tarun-joy]

Summary

• publish a versioned runtime API for animation metadata, exact frame rendering, current selection, and session-only application
• restore transient thinking labels when reasoning ends instead of leaving stopped animation frames in the transcript
• gate the AssistantMessageComponent patch to active reasoning and support safe reload over the legacy boolean patch marker
• clear both single-line working messages and multi-line widgets on stop
• update lifecycle handling for current Pi (session_shutdown replaces removed session_switch)

Motivation

Settings integrations need an exact live preview without copying all 26 renderers. The previous thinking-label patch also animated completed/history labels and intentionally retained the final frame, leaving static pulse rows in the transcript.

Validation

• strict TypeScript check passes with zero diagnostics against Pi 0.84 types
• isolated Pi RPC smoke loads the package with zero errors
• runtime smoke verifies API v1, all 26 metadata entries, exact frame rendering, legacy-patch upgrade, historical-label gating, active animation, restoration, and disable cleanup