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

turbo.json

@@ -0,0 +1,18 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "outputs": ["dist/**", ".output/**", ".nuxt/**"]
+    },
+    "dev": {
+      "cache": false,
+      "persistent": true
+    },
+    "lint": {},
+    "format": {},
+    "type-check": {
+      "dependsOn": ["^build"]
+    }
+  }
+}