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>

turbo.json

@@ -0,0 +1,26 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "ui": "tui",
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$", ".env*"],
+      "outputs": ["dist/**"]
+    },
+    "lint": {
+      "dependsOn": ["^lint"]
+    },
+    "typecheck": {
+      "dependsOn": ["^typecheck"]
+    },
+    "test": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$"],
+      "outputs": ["coverage/**"]
+    },
+    "dev": {
+      "cache": false,
+      "persistent": true
+    }
+  }
+}