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/lib/game/store.ts

@@ -813,6 +813,7 @@ interface GameStore extends GameState, CraftingActions {
   
   // Spire Mode actions
   enterSpireMode: () => void;
+  climbDownFloor: () => void;  // Climb down one floor at a time
   exitSpireMode: () => void;
 }
 
@@ -2018,13 +2019,51 @@ export const useGameStore = create<GameStore>()(
         }));
       },
 
-      // Exit Spire Mode - return to normal game UI
+      // Climb down one floor (for Spire Mode)
+      climbDownFloor: () => {
+        set((state) => {
+          const newFloor = Math.max(1, state.currentFloor - 1);
+          if (newFloor === state.currentFloor) {
+            // Already at floor 1, can't go down further
+            return state;
+          }
+          
+          // Mark current floor as cleared (it will respawn when we come back)
+          const clearedFloors = { ...state.clearedFloors };
+          clearedFloors[state.currentFloor] = true;
+          
+          // Check if new floor was cleared (needs respawn)
+          const newFloorCleared = clearedFloors[newFloor];
+          if (newFloorCleared) {
+            delete clearedFloors[newFloor];
+          }
+          
+          return {
+            currentFloor: newFloor,
+            floorMaxHP: getFloorMaxHP(newFloor),
+            floorHP: getFloorMaxHP(newFloor),
+            maxFloorReached: Math.max(state.maxFloorReached, newFloor),
+            clearedFloors,
+            climbDirection: 'down' as const,
+            equipmentSpellStates: state.equipmentSpellStates.map(s => ({ ...s, castProgress: 0 })),
+            log: [`⬇️ Climbed down to floor ${newFloor}${newFloorCleared ? ' (respawned)' : ''}.`, ...state.log.slice(0, 49)],
+          };
+        });
+      },
+
+      // Exit Spire Mode - only works when at floor 1
       exitSpireMode: () => {
-        set((state) => ({
-          spireMode: false,
-          currentAction: 'meditate',
-          log: ['⬇️ Climbed down from the Spire. Returning to normal view.', ...state.log.slice(0, 49)],
-        }));
+        set((state) => {
+          // Only allow exit if at floor 1 (bottom)
+          if (state.currentFloor > 1) {
+            return state; // Can't exit, need to climb down to floor 1 first
+          }
+          return {
+            spireMode: false,
+            currentAction: 'meditate',
+            log: ['⬇️ Climbed down from the Spire. Returning to normal view.', ...state.log.slice(0, 49)],
+          };
+        });
       },
 
       togglePause: () => {