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

.gitignore

@@ -0,0 +1,45 @@
+# Dependencies
+node_modules
+
+# Build outputs
+dist
+.output
+.nuxt
+.nitro
+.data
+.cache
+
+# TypeScript
+*.tsbuildinfo
+
+# Logs
+logs
+*.log
+npm-debug.log*
+pnpm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# Environment
+.env
+.env.local
+.env.*.local
+
+# OS
+.DS_Store
+
+# IDE
+.idea
+.vscode/*
+!.vscode/settings.json
+!.vscode/extensions.json
+
+# Coverage
+coverage
+
+# Nuxt
+.output
+.nuxt
+.nitro
+.cache