Fix Sub-Task 1: Spire UI Fixes (Bugs 1, 2, 3)

- Bug 1: Floor health display now reactive (uses Zustand store properly)
- Bug 2: Climb Down button now climbs floor-by-floor, exit only at floor 1
- Bug 3: Redesigned SpireTab as Spire Stats view, moved Enter Spire Mode button to SpireTab, moved activity log to SpireModeUI

Changes:
- Added climbDownFloor() action to store.ts
- Modified exitSpireMode() to only work at floor 1
- Updated SpireTab.tsx: removed Current Floor stat, added Enter Spire Mode button
- Updated page.tsx: Climb Down climbs one floor, added Exit Spire button at floor 1, moved activity log to SpireModeUI

src/app/page.tsx

@@ -254,21 +254,57 @@ export default function ManaLoopGame() {
               <DebugName name="SpireModeUI">
                 <div className="flex items-center justify-between mb-4">
                   <h2 className="text-2xl font-bold game-title text-amber-400">
-                    🏔️ Spire Mode
+                    🏔️ Spire Mode - Floor {store.currentFloor}
                   </h2>
-                  <Button
-                    variant="outline"
-                    className="border-blue-600/50 text-blue-400 hover:bg-blue-900/20"
-                    onClick={() => store.exitSpireMode()}
-                  >
-                    <ChevronDown className="w-4 h-4 mr-2" />
-                    Climb Down
-                  </Button>
+                  <div className="flex gap-2">
+                    <Button
+                      variant="outline"
+                      className="border-blue-600/50 text-blue-400 hover:bg-blue-900/20"
+                      onClick={() => store.climbDownFloor()}
+                    >
+                      <ChevronDown className="w-4 h-4 mr-2" />
+                      Climb Down
+                    </Button>
+                    {store.currentFloor === 1 ? (
+                      <Button
+                        variant="default"
+                        className="bg-green-600 hover:bg-green-700"
+                        onClick={() => store.exitSpireMode()}
+                      >
+                        Exit Spire
+                      </Button>
+                    ) : (
+                      <span className="text-xs text-gray-400 flex items-center">
+                        Reach floor 1 to exit
+                      </span>
+                    )}
+                  </div>
                 </div>
                 
                 <Suspense fallback={<TabLoadingFallback />}>
                   <SpireTab store={store} simpleMode={true} />
                 </Suspense>
+                
+                {/* Activity Log for Spire Mode */}
+                <Card className="bg-gray-900/80 border-gray-700">
+                  <CardHeader className="pb-2">
+                    <CardTitle className="text-amber-400 game-panel-title text-xs">Activity Log</CardTitle>
+                  </CardHeader>
+                  <CardContent>
+                    <ScrollArea className="h-32">
+                      <div className="space-y-1">
+                        {store.log.slice(0, 20).map((entry, i) => (
+                          <div
+                            key={i}
+                            className={`text-sm ${i === 0 ? 'text-gray-200' : 'text-gray-500'} italic`}
+                          >
+                            {entry}
+                          </div>
+                        ))}
+                      </div>
+                    </ScrollArea>
+                  </CardContent>
+                </Card>
               </DebugName>
             </div>
           ) : (