feat(frontend): Add generations counter to inform frontends when a list should be re-rendered.

crates/pikl-core/src/model/event.rs

@@ -72,6 +72,10 @@ pub struct ViewState {
     pub total_items: usize,
     pub total_filtered: usize,
     pub mode: Mode,
+    /// Monotonically increasing counter. Each call to
+    /// `build_view_state()` bumps this, so frontends can
+    /// detect duplicate broadcasts and skip redundant redraws.
+    pub generation: u64,
 }
 
 /// A single item in the current viewport window. Has the