Validate action targets; format timestamps client-side; clippy cleanup

- A dangling alternative.action (navigating to "Nothing here") is now
  a lint/load-time rejection like any other dead reference.
- Rows re-rendered after a client-side refetch showed raw milliseconds
  - format_ms now formats via js_sys::Date under hydrate, matching the
  server's rendering.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app.rs

@@ -492,7 +492,7 @@ fn AlternativeCard(
     for feature in &alternative.features {
         for req in &feature.requirements {
             if req.kind == "file" {
-                file_refs.entry(req.name.clone()).or_insert_with(NodeRef::new);
+                file_refs.entry(req.name.clone()).or_default();
             } else if req.kind == "select" {
                 select_field_map
                     .entry(req.name.clone())
@@ -1335,7 +1335,21 @@ fn format_ms(ms: i64) -> String {
             .map(|t| t.format("%Y-%m-%d %H:%M UTC").to_string())
             .unwrap_or_else(|| ms.to_string())
     }
-    #[cfg(not(feature = "ssr"))]
+    // Rows re-rendered client-side (a post-confirm refetch) format
+    // here, not on the server - raw milliseconds would show otherwise.
+    #[cfg(all(not(feature = "ssr"), feature = "hydrate"))]
+    {
+        let date = js_sys::Date::new(&wasm_bindgen::JsValue::from_f64(ms as f64));
+        format!(
+            "{:04}-{:02}-{:02} {:02}:{:02} UTC",
+            date.get_utc_full_year(),
+            date.get_utc_month() + 1,
+            date.get_utc_date(),
+            date.get_utc_hours(),
+            date.get_utc_minutes(),
+        )
+    }
+    #[cfg(all(not(feature = "ssr"), not(feature = "hydrate")))]
     {
         ms.to_string()
     }