feat(ui-calculator): input validation, load caps, ceil display, modernization layout

- custom load capped at cargo capacity (error when exceeded); full load shows the cargo capacity; zero cargo pins load to empty and disables the toggle

- per-input red border + tooltip for every invalid value (blocks, techs, load, MAT, modernization target); no value may be negative; locking a speed is disabled when drive is zero

- display every computed number (results + goal-seek back-solved input) rounded up to 3 decimals via a shared pkg/calc Ceil3 bridged to wasm; engine keeps its own round-to-nearest util.Fixed*

- modernization total upgrade cost spans two columns (single line)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/lib/util/ship-class-validation.ts

@@ -170,3 +170,35 @@ function isValidDWSC(value: number): boolean {
 	if (!Number.isFinite(value)) return false;
 	return value === 0 || value >= 1;
 }
+
+/**
+ * shipClassFieldErrors returns the invalid reason for each offending
+ * block, independently, so the calculator can mark every bad input
+ * (not just the first failure `validateShipClassValues` reports). The
+ * weapons/armament pairing rule flags both fields. The all-zero rule is
+ * a whole-design condition and is left to `validateShipClassValues`.
+ */
+export function shipClassFieldErrors(
+	values: ShipClassValues,
+): Partial<Record<keyof ShipClassValues, ShipClassValueInvalidReason>> {
+	const errors: Partial<
+		Record<keyof ShipClassValues, ShipClassValueInvalidReason>
+	> = {};
+	if (!isValidDWSC(values.drive)) errors.drive = "drive_value";
+	if (!Number.isFinite(values.armament) || values.armament < 0) {
+		errors.armament = "armament_value";
+	} else if (!Number.isInteger(values.armament)) {
+		errors.armament = "armament_not_integer";
+	}
+	if (!isValidDWSC(values.weapons)) errors.weapons = "weapons_value";
+	if (!isValidDWSC(values.shields)) errors.shields = "shields_value";
+	if (!isValidDWSC(values.cargo)) errors.cargo = "cargo_value";
+	if (
+		(values.armament === 0 && values.weapons !== 0) ||
+		(values.armament !== 0 && values.weapons === 0)
+	) {
+		errors.weapons ??= "armament_weapons_pair";
+		errors.armament ??= "armament_weapons_pair";
+	}
+	return errors;
+}