feat(config): add MosaicConfig schema + loader with tier auto-detection

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

packages/config/package.json

@@ -0,0 +1,35 @@
+{
+  "name": "@mosaic/config",
+  "version": "0.0.1",
+  "type": "module",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "default": "./dist/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "lint": "eslint src",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run --passWithNoTests"
+  },
+  "dependencies": {
+    "@mosaic/memory": "workspace:^",
+    "@mosaic/queue": "workspace:^",
+    "@mosaic/storage": "workspace:^"
+  },
+  "devDependencies": {
+    "typescript": "^5.8.0",
+    "vitest": "^2.0.0"
+  },
+  "publishConfig": {
+    "registry": "https://git.mosaicstack.dev/api/packages/mosaic/npm/",
+    "access": "public"
+  },
+  "files": [
+    "dist"
+  ]
+}