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>

.lintstagedrc

@@ -0,0 +1,9 @@
+{
+  "**/*.{ts,tsx,js,jsx}": [
+    "prettier --write",
+    "eslint --fix"
+  ],
+  "**/*.{json,md,yaml,yml}": [
+    "prettier --write"
+  ]
+}