chore: scaffold mosaic monorepo (Phase 0)

- pnpm workspaces + Turborepo
- tsconfig.base.json strict ESM
- @mosaic/types stub package
- Woodpecker CI pipeline with Valkey service
- docs/PRD.md, docs/TASKS.md, CONTEXT.md

packages/types/README.md

@@ -0,0 +1,3 @@
+# @mosaic/types
+
+Shared type definitions for the Mosaic package ecosystem.

packages/types/package.json

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+{
+  "name": "@mosaic/types",
+  "version": "0.1.0",
+  "private": false,
+  "type": "module",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "files": [
+    "dist",
+    "README.md"
+  ],
+  "scripts": {
+    "build": "tsc -p tsconfig.json",
+    "test": "echo \"No tests for @mosaic/types\"",
+    "lint": "echo \"No lint configured for @mosaic/types\"",
+    "typecheck": "tsc -p tsconfig.json --noEmit"
+  }
+}

packages/types/src/index.ts

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+// @mosaic/types - shared type definitions
+export type Placeholder = Record<string, never>;

packages/types/tsconfig.json

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+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src/**/*.ts"]
+}