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

packages/tsconfig/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "@inkreach/tsconfig",
+  "version": "0.0.0",
+  "private": true,
+  "files": ["base.json", "api.json", "vue.json"]
+}