ui/phase-18: ship-class calc bridge with live designer preview

Wires pkg/calc/ship.go into the WASM Core boundary as seven thin
wrappers (DriveEffective, EmptyMass, WeaponsBlockMass, FullMass,
Speed, CargoCapacity, CarryingMass). The ship-class designer reads
Core through a new CORE_CONTEXT_KEY populated by the in-game layout
and renders a five-row preview pane (mass, full-load mass, max
speed, range at full load, cargo capacity) that updates reactively
on every form edit and on the player's localPlayer{Drive,Weapons,
Shields,Cargo} tech levels — three of which are now decoded from
the report's Player block alongside the existing localPlayerDrive.

CarryingMass is the seventh wrapper added to the original six-function
list so that "full-load mass" composes through pkg/calc/ functions
without putting math in TypeScript.

ui/frontend/src/lib/core-context.svelte.ts

@@ -0,0 +1,31 @@
+// Exposes the WASM `Core` instance through a Svelte context so views
+// that need its math bridge (Phase 18 ship-class preview, future
+// inspector calculators) can read it without re-booting the module.
+// The layout populates `core` after `loadCore()` resolves; consumers
+// observe `null` while the boot is in flight and the live `Core`
+// once the runtime is ready.
+
+import type { Core } from "../platform/core/index";
+
+/**
+ * CORE_CONTEXT_KEY is the Svelte context key the in-game shell
+ * layout uses to expose its booted `Core` to descendants such as
+ * the ship-class designer preview pane.
+ */
+export const CORE_CONTEXT_KEY = Symbol("core");
+
+export interface CoreHandle {
+	readonly core: Core | null;
+}
+
+export class CoreHolder implements CoreHandle {
+	#core: Core | null = $state(null);
+
+	get core(): Core | null {
+		return this.#core;
+	}
+
+	set(core: Core | null): void {
+		this.#core = core;
+	}
+}