feat(P0-001): scaffold monorepo structure

pnpm workspaces, Turborepo, TypeScript strict, ESLint flat config,
Prettier, Vitest, husky + lint-staged. Placeholder packages for all
16 packages + 2 apps + 2 plugins.

Closes #1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.prettierrc

@@ -0,0 +1,6 @@
+{
+  "singleQuote": true,
+  "trailingComma": "all",
+  "semi": true,
+  "printWidth": 100
+}