fix(ruview-swarm): clippy manual_is_multiple_of in lawnmower planner

CI `clippy (-D warnings, --no-deps)` failed on patterns.rs:131 —
`row % 2 == 0` is flagged by clippy::manual_is_multiple_of. Use
`row.is_multiple_of(2)` (identical even-row check). Both CI clippy
variants (--no-default-features and --features full,train) now pass.

Co-Authored-By: claude-flow <ruv@ruv.net>

v2/crates/ruview-swarm/src/planning/patterns.rs

@@ -128,7 +128,7 @@ fn serpentine_in_region(
     let y = y.min(y1);
 
     // Serpentine: even rows L→R, odd rows R→L.
-    let along = if row % 2 == 0 { col } else { cols - 1 - col };
+    let along = if row.is_multiple_of(2) { col } else { cols - 1 - col };
     let x = x0 + (along as f64 + 0.5) * scan_width_m;
     let x = x.min(x1);