fix: capacities single-sourced in types (display MAX_WINDOWS/BUFFER_PAGES, storage MAX_CLIENTS), display + storage budgets derived from them, const asserts on VA layouts; kernel regions 64 -> 256

crates/domain/src/memory/mod.rs

@@ -18,7 +18,8 @@ mod quota_tests;
 #[path = "tests.rs"]
 mod tests;
 
-pub const MAX_REGIONS: usize = if cfg!(kani) { 1 } else { 64 };
+/// System-wide: the display and storage hold a dozen or more each.
+pub const MAX_REGIONS: usize = if cfg!(kani) { 1 } else { 256 };
 pub const MAX_REGION_MAPPINGS: usize = if cfg!(kani) { 2 } else { 4 };
 
 /// Where a region's frames come from.