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.

build.rs

@@ -1,3 +1,26 @@
+use std::env;
+use std::fs;
+use std::path::Path;
+
 fn main() {
     println!("cargo:rerun-if-changed=migrations");
+
+    let root_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+    let root_dir = Path::new(&root_dir);
+    let dir = root_dir.join("static/js");
+
+    let entries = fs::read_dir(&dir).unwrap();
+
+    let js_bundles: Vec<String> = entries
+        .filter_map(Result::ok)
+        .filter(|entry| entry.file_name().to_string_lossy().ends_with(".js"))
+        .map(|entry| {
+            Path::new("/")
+                .join(entry.path().strip_prefix(root_dir).unwrap())
+                .display()
+                .to_string()
+        })
+        .collect();
+
+    fs::write(dir.join("js_bundles.txt"), js_bundles.join("\n")).unwrap();
 }