Add frontend JS and improve post styling

Frontend is built with Bun. It uses Stimulus to progressively enhance
the server-built HTML. Currently, it only replaces UTC timestamps from
the server with the time in the browser's timezone.

frontend/tsconfig.json

@@ -0,0 +1,22 @@
+{
+  "compilerOptions": {
+    "lib": ["ESNext", "dom"],
+    "module": "esnext",
+    "target": "esnext",
+    "moduleResolution": "node",
+    "moduleDetection": "force",
+    "allowImportingTsExtensions": true,
+    "strict": true,
+    "downlevelIteration": true,
+    "skipLibCheck": true,
+    "jsx": "preserve",
+    "allowSyntheticDefaultImports": true,
+    "forceConsistentCasingInFileNames": true,
+    "allowJs": true,
+    "noEmit": true,
+    "types": [
+       // disabled because of https://github.com/oven-sh/bun/issues/3030
+       // "bun-types" // add Bun global
+    ]
+  }
+}