feat: replace sidebar row icon with prefix and suffix slots

docs/CHECKLIST.md

@@ -9,6 +9,13 @@ is the first downstream consumer; its screens drive the order.
 
 ## Next
 
+- [ ] **Declarative render audit** — run the AGENTS.md render rule over the
+      other landed components: replace `let mut` element variables reassigned
+      under `if` / `if let` with one chained expression using `.when(...)` /
+      `.when_some(...)` / `.map(...)`. The sidebar row is the model; sweep
+      `crates/core`, `crates/data`, `crates/editor`, `crates/layout`, and
+      re-run tests plus a gallery pass after each crate.
+
 ## Queue — to follow
 
 Platform metric adoption continues one component at a time; each stop goes