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

tsconfig.base.json

@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "strict": true,
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "outDir": "dist",
+    "esModuleInterop": true,
+    "skipLibCheck": true
+  }
+}