fix(simulation): resolve clippy warnings in atlas modules

Replace HashMap/HashSet with BTreeMap/BTreeSet per D-030 determinism
rule. Fix while_let_loop, map_or simplification, collapsible if,
unsigned_abs casting, iterator indexing, and redundant wildcard arms.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/atlas/district_mix.rs

@@ -92,7 +92,7 @@ fn role_row(economic_role: &str) -> usize {
         "transit_hub" => 6,
         "research" => 7,
         "military" => 8,
-        "residential" | _ => 9,
+        _ => 9,
     }
 }