chore: migrate to pnpm workspaces monorepo with Turborepo

- Restructure directories: apps/api, apps/admin, apps/website
- Add root pnpm-workspace.yaml, turbo.json, .prettierrc, .gitignore
- Rename packages to @inkreach/api, @inkreach/admin, @inkreach/website
- Add shared packages: packages/tsconfig, packages/shared-types
- Add pnpm.onlyBuiltDependencies for native builds
- Update docs: README.md, structs.md
- All three projects build successfully

apps/admin/package.json

@@ -0,0 +1,32 @@
+{
+  "name": "@inkreach/admin",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vue-tsc -b && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@element-plus/icons-vue": "^2.3.2",
+    "@vueuse/core": "^14.3.0",
+    "axios": "^1.18.0",
+    "dayjs": "^1.11.21",
+    "element-plus": "^2.14.2",
+    "pinia": "^3.0.4",
+    "vue": "^3.5.34",
+    "vue-router": "^4.6.4"
+  },
+  "devDependencies": {
+    "@types/node": "^24.12.3",
+    "@vitejs/plugin-vue": "^6.0.6",
+    "@vue/tsconfig": "^0.9.1",
+    "sass": "^1.101.0",
+    "typescript": "~6.0.2",
+    "unplugin-auto-import": "^21.0.0",
+    "unplugin-vue-components": "^32.1.0",
+    "vite": "^8.0.12",
+    "vue-tsc": "^3.2.8"
+  }
+}