feat(tools): implement advanced brush tools - Clone Stamp, Smudge, and Dodge/Burn

Added three professional-grade image manipulation tools to complete Feature 4:

Clone Stamp Tool (Shortcut: 8)
- Sample from source location with Alt+Click
- Paint sampled content to destination
- Maintains relative offset for natural cloning
- Supports soft/hard brush with hardness setting

Smudge Tool (Shortcut: 9)
- Creates realistic paint-smearing effects
- Progressively blends colors for natural smudging
- Uses flow setting to control smudge strength
- Soft brush falloff for smooth blending

Dodge/Burn Tool (Shortcut: 0)
- Dodge mode: Lightens image areas (default)
- Burn mode: Darkens image areas (Alt key)
- Professional photography exposure adjustment
- Respects hardness setting for precise control

All tools:
- Fully integrated with tool palette and keyboard shortcuts
- Support smooth interpolation for fluid strokes
- Use existing tool settings (size, opacity, hardness, flow, spacing)
- Lazy-loaded via code splitting system
- Icons from Lucide React (Stamp, Droplet, Sun)

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

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

lib/tool-loader.ts

@@ -93,6 +93,21 @@ async function loadTool(toolKey: string): Promise<BaseTool> {
         tool = new TextTool();
         break;
       }
+      case 'clone': {
+        const { CloneStampTool } = await import('@/tools/clone-stamp-tool');
+        tool = new CloneStampTool();
+        break;
+      }
+      case 'smudge': {
+        const { SmudgeTool } = await import('@/tools/smudge-tool');
+        tool = new SmudgeTool();
+        break;
+      }
+      case 'dodge': {
+        const { DodgeBurnTool } = await import('@/tools/dodge-burn-tool');
+        tool = new DodgeBurnTool();
+        break;
+      }
       default: {
         // Fallback to pencil tool
         const { PencilTool } = await import('@/tools/pencil-tool');