web: vite + react + tailwind hello page with dark-mode toggle

Workspace packages export TS source under a 'source' condition used by
vite, node (--conditions=source) and tsc.

Task: M0-T4

packages/shared/package.json

@@ -7,7 +7,7 @@
   "exports": {
     ".": {
       "types": "./src/index.ts",
-      "development": "./src/index.ts",
+      "source": "./src/index.ts",
       "default": "./dist/index.js"
     }
   },