Add SAM Smart Select and AI Inpaint tools to miniPaint

New features:
- Smart Select tool: Click to select objects using SAM (Segment Anything)
- AI Inpaint tool: Edit selected regions with text prompts

Changes:
- frontend/src/js/tools/smart_select.js: SAM-powered selection tool
- frontend/src/js/tools/ai_inpaint.js: AI inpainting with prompt dialog
- frontend/src/js/services/api.js: API service for backend communication
- frontend/src/js/config.js: Register new tools
- frontend/src/css/layout.css: Tool icon styles
- frontend/images/icons/: SVG icons for new tools
- backend/app/routers/tools.py: New base64 API endpoints
- frontend/Dockerfile: Updated for miniPaint build
- frontend/nginx.conf: Added /api prefix proxy

frontend/nginx.conf

@@ -70,6 +70,18 @@ server {
         proxy_pass http://backend:8000;
     }
 
+    # API prefix for frontend (maps /api/tools to /tools, etc.)
+    location /api/ {
+        rewrite ^/api/(.*)$ /$1 break;
+        proxy_pass http://backend:8000;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection 'upgrade';
+        proxy_set_header Host $host;
+        proxy_cache_bypass $http_upgrade;
+        proxy_read_timeout 300s;
+    }
+
     location /docs {
         proxy_pass http://backend:8000;
     }