Initial commit: Cosmic Garden idle game foundation

- Complete game architecture with modular JS structure
- 12 buildings across 4 tiers with scaling costs
- 15+ upgrades with requirements and bonuses
- 20 achievements to unlock
- Auto-save system with offline progress (50% efficiency)
- Export/Import save functionality
- Responsive dark-themed UI with cosmic aesthetic
- Floating text animations and notification system

js/saveSystem.js

@@ -0,0 +1,104 @@
+/**
+ * Cosmic Garden - Save System
+ * Handles localStorage persistence and export/import
+ */
+
+const SaveSystem = {
+    SAVE_KEY: 'cosmicGardenSave',
+
+    /**
+     * Save game to localStorage
+     */
+    save() {
+        const data = JSON.stringify(Game.state);
+        localStorage.setItem(this.SAVE_KEY, data);
+        console.log('💾 Game saved');
+    },
+
+    /**
+     * Load game from localStorage
+     */
+    load() {
+        const data = localStorage.getItem(this.SAVE_KEY);
+        if (data) {
+            try {
+                return JSON.parse(data);
+            } catch (e) {
+                console.error('Failed to parse save:', e);
+                return null;
+            }
+        }
+        return null;
+    },
+
+    /**
+     * Export save as base64 string
+     */
+    exportSave() {
+        const data = btoa(JSON.stringify(Game.state));
+        navigator.clipboard.writeText(data).then(() => {
+            UI.showNotification('Save copied to clipboard!', 'success');
+        }).catch(() => {
+            // Fallback for older browsers
+            const textarea = document.createElement('textarea');
+            textarea.value = data;
+            document.body.appendChild(textarea);
+            textarea.select();
+            document.execCommand('copy');
+            document.body.removeChild(textarea);
+            UI.showNotification('Save copied to clipboard!', 'success');
+        });
+    },
+
+    /**
+     * Import save from base64 string
+     */
+    importSave(data) {
+        try {
+            const parsed = JSON.parse(atob(data));
+            
+            // Validate save data
+            if (!parsed.stardust || !parsed.buildings) {
+                throw new Error('Invalid save format');
+            }
+            
+            // Merge with existing state
+            Game.state = { ...Game.state, ...parsed };
+            Game.state.lastSaveTime = Date.now();
+            
+            UI.update();
+            return true;
+        } catch (e) {
+            console.error('Failed to import save:', e);
+            UI.showNotification('Invalid save data!', 'warning');
+            return false;
+        }
+    },
+
+    /**
+     * Clear save data
+     */
+    clear() {
+        localStorage.removeItem(this.SAVE_KEY);
+    },
+
+    /**
+     * Get last save time
+     */
+    getLastSaveTime() {
+        const data = this.load();
+        if (data && data.lastSaveTime) {
+            return new Date(data.lastSaveTime);
+        }
+        return null;
+    },
+
+    /**
+     * Check if auto-save is available
+     */
+    hasAutoSave() {
+        return !!localStorage.getItem(this.SAVE_KEY);
+    }
+};
+
+window.SaveSystem = SaveSystem;