feat: expansion coming-soon preview with save-safe display data

Add an expansion preview system so the Goddess and Vampire panels render
their full content (zones, bosses, thralls, achievements, etc.) even when the
expansion has not been unlocked, with all interactive elements visually
disabled.

- API /load now returns expansionPreview alongside game state, populated from
  initialGoddessState() and initialVampireState() — never part of the saved blob
- LoadResponse type updated with expansionPreview field
- gameContext exposes goddessPreview and vampirePreview, stored in separate
  state vars that never touch stateReference so saves are never polluted
- gameLayout applies expansion-preview CSS class when viewing a locked expansion
  with preview data available, and shows the coming-soon banner
- All 22 expansion panels updated to use state.vampire ?? vampirePreview and
  state.goddess ?? goddessPreview for display
- CSS disables all buttons/inputs/selects inside .expansion-preview
- apotheosis service patched to never auto-initialise goddess state — expansion
  remains locked until explicitly released

apps/web/src/components/game/vampireThrallsPanel.tsx

@@ -198,7 +198,9 @@ const ThrallCard = ({
  * @returns The JSX element.
  */
 const VampireThrallsPanel = (): JSX.Element => {
-  const { state, formatNumber, toggleVampireAutoThrall } = useGame();
+  const {
+    state, formatNumber, toggleVampireAutoThrall, vampirePreview,
+  } = useGame();
   const [ selectedBatch, setSelectedBatch ] = useState<BatchSize>(() => {
     return parseBatchSize(localStorage.getItem("elysium_thrall_batch"));
   });
@@ -211,7 +213,7 @@ const VampireThrallsPanel = (): JSX.Element => {
     );
   }
 
-  const vampireState = state.vampire;
+  const vampireState = state.vampire ?? vampirePreview;
   if (vampireState === undefined) {
     return (
       <section className="panel">