Timeline: config-driven mute rules; show replies with thread-root context

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DgBEW6qAwgn2fcQbA2f4ZQ

shared/types.ts

@@ -59,6 +59,8 @@ export interface TimelineEvent {
   reviewState: string | null;
   path: string | null;
   read: boolean;
+  /** Set when this is a reply within a review thread: the thread's root comment. */
+  inReplyTo: { actor: string; bodyExcerpt: string } | null;
 }
 
 export interface StatePayload {