feat(phase-13): implement brush presets system

Add comprehensive brush presets system for saving and loading brush configurations.

Features:
- Brush presets store with persistence
- 5 default presets included:
  * Hard Brush - Solid, precise edges
  * Soft Brush - Smooth, gradual falloff
  * Airbrush - Low opacity, soft flow
  * Pencil - Tiny, hard, precise
  * Ink - Medium, slightly soft
- Preset management functions:
  * addPreset() - Save current brush settings
  * removePreset() - Delete preset
  * updatePreset() - Modify preset
  * setActivePreset() - Select active preset
  * getPreset() - Get preset by ID
  * clearPresets() - Reset to defaults
- Each preset stores:
  * size, opacity, hardness, flow, spacing
  * Unique ID and creation timestamp
- localStorage persistence
- Active preset tracking

Changes:
- Created store/brush-presets-store.ts
- BrushPreset interface with settings
- Exported from store/index.ts
- Ready for UI integration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

store/brush-presets-store.ts

@@ -0,0 +1,152 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+import type { ToolSettings } from '@/types';
+
+export interface BrushPreset {
+  id: string;
+  name: string;
+  settings: Partial<ToolSettings>;
+  createdAt: number;
+}
+
+interface BrushPresetsStore {
+  /** All brush presets */
+  presets: BrushPreset[];
+  /** Currently selected preset ID */
+  activePresetId: string | null;
+
+  /** Add a new preset */
+  addPreset: (name: string, settings: Partial<ToolSettings>) => BrushPreset;
+  /** Remove a preset */
+  removePreset: (id: string) => void;
+  /** Update a preset */
+  updatePreset: (id: string, name: string, settings: Partial<ToolSettings>) => void;
+  /** Set active preset */
+  setActivePreset: (id: string | null) => void;
+  /** Get preset by ID */
+  getPreset: (id: string) => BrushPreset | undefined;
+  /** Clear all presets */
+  clearPresets: () => void;
+}
+
+// Default presets
+const DEFAULT_PRESETS: Omit<BrushPreset, 'id' | 'createdAt'>[] = [
+  {
+    name: 'Hard Brush',
+    settings: {
+      size: 10,
+      opacity: 1,
+      hardness: 1,
+      flow: 1,
+      spacing: 0.25,
+    },
+  },
+  {
+    name: 'Soft Brush',
+    settings: {
+      size: 30,
+      opacity: 1,
+      hardness: 0,
+      flow: 1,
+      spacing: 0.25,
+    },
+  },
+  {
+    name: 'Airbrush',
+    settings: {
+      size: 50,
+      opacity: 0.3,
+      hardness: 0,
+      flow: 0.5,
+      spacing: 0.1,
+    },
+  },
+  {
+    name: 'Pencil',
+    settings: {
+      size: 2,
+      opacity: 1,
+      hardness: 1,
+      flow: 1,
+      spacing: 0.1,
+    },
+  },
+  {
+    name: 'Ink',
+    settings: {
+      size: 5,
+      opacity: 1,
+      hardness: 0.8,
+      flow: 1,
+      spacing: 0.15,
+    },
+  },
+];
+
+export const useBrushPresetsStore = create<BrushPresetsStore>()(
+  persist(
+    (set, get) => ({
+      presets: DEFAULT_PRESETS.map((preset, index) => ({
+        ...preset,
+        id: `default-${index}`,
+        createdAt: Date.now() - (DEFAULT_PRESETS.length - index) * 1000,
+      })),
+      activePresetId: null,
+
+      addPreset: (name, settings) => {
+        const now = Date.now();
+        const preset: BrushPreset = {
+          id: `preset-${now}`,
+          name,
+          settings,
+          createdAt: now,
+        };
+
+        set((state) => ({
+          presets: [...state.presets, preset],
+        }));
+
+        return preset;
+      },
+
+      removePreset: (id) => {
+        set((state) => ({
+          presets: state.presets.filter((p) => p.id !== id),
+          activePresetId: state.activePresetId === id ? null : state.activePresetId,
+        }));
+      },
+
+      updatePreset: (id, name, settings) => {
+        set((state) => ({
+          presets: state.presets.map((p) =>
+            p.id === id
+              ? { ...p, name, settings }
+              : p
+          ),
+        }));
+      },
+
+      setActivePreset: (id) => {
+        set({ activePresetId: id });
+      },
+
+      getPreset: (id) => {
+        return get().presets.find((p) => p.id === id);
+      },
+
+      clearPresets: () => {
+        set({
+          presets: DEFAULT_PRESETS.map((preset, index) => ({
+            ...preset,
+            id: `default-${index}`,
+            createdAt: Date.now() - (DEFAULT_PRESETS.length - index) * 1000,
+          })),
+          activePresetId: null,
+        });
+      },
+    }),
+    {
+      name: 'brush-presets-storage',
+    }
+  )
+);

store/index.ts

@@ -13,3 +13,4 @@ export * from './toast-store';
 export * from './context-menu-store';
 export * from './guides-store';
 export * from './recent-files-store';
+export * from './brush-presets-store';