refactor: consolidate backend/frontend, remove api/web duplicates

- backend/ kept as canonical, api/ features merged (EBook, ReadingProgress, ReadingSettings)
- frontend/ kept as canonical, web/ pages merged (Library, Reader, AddBook, Auth, Settings)
- Added Dockerfiles for backend/ and frontend/
- Updated docker-compose.yml for consolidated services
- Updated README, package.json workspaces
- api/ and web/ directories removed

package.json

@@ -3,10 +3,7 @@
   "version": "1.0.0",
   "private": true,
   "workspaces": [
-    "web"
-  ],
-  "scripts": {
-    "dev": "yarn --cwd web dev",
-    "build": "yarn --cwd web build"
-  }
+    "frontend",
+    "backend"
+  ]
 }