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

tsconfig.base.json

@@ -10,7 +10,7 @@
     "verbatimModuleSyntax": true,
     "allowImportingTsExtensions": true,
     "rewriteRelativeImportExtensions": true,
-    "customConditions": ["development"],
+    "customConditions": ["source"],
     "skipLibCheck": true,
     "isolatedModules": true
   }