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/content.rs

@@ -233,11 +233,8 @@ impl Requirement {
     }
 }
 
-/// Extracts `scheme://host` from a repo's normal browser URL (e.g.
-/// `https://project.uhhm.no/uhhm/questions` -> `https://project.uhhm.no`)
-/// - the Gitea API base every helper in this module builds requests
-/// against, including ones (like `resolve_gitea_repo`) that have
-/// nothing to do with content loading, just the same Gitea instance.
+/// Extracts `scheme://host` from a repo's normal browser URL - the
+/// Gitea API base every helper in this module builds requests against.
 #[cfg(feature = "ssr")]
 pub fn gitea_api_base(repo_url: &str) -> anyhow::Result<String> {
     let parsed = url::Url::parse(repo_url)
@@ -407,6 +404,16 @@ pub fn validate_questions(
 ) -> anyhow::Result<()> {
     for question in questions.values() {
         for alternative in &question.alternatives {
+            // A dangling action is a literal dead end: the submit
+            // button navigates to "Nothing here".
+            if let Some(action) = &alternative.action {
+                if !questions.contains_key(action) {
+                    anyhow::bail!(
+                        "question {:?} alternative {:?}: action {:?} does not match any declared question id",
+                        question.id, alternative.name, action
+                    );
+                }
+            }
             if let Some(st) = &alternative.self_transition {
                 if let Some(schema) = aggregates.get(&st.bucket) {
                     if !schema.has_state(&st.to) {
@@ -727,4 +734,23 @@ alternatives:
         let err = validate_questions(&questions, &schema_fixture()).unwrap_err();
         assert!(err.to_string().contains("not a declared edge"));
     }
+
+    #[test]
+    fn dangling_action_is_rejected() {
+        let question: Question =
+            serde_yaml::from_str("id: /a\nname: A\nalternatives:\n  - name: Go\n    action: /nowhere\n")
+                .unwrap();
+        let questions = std::collections::HashMap::from([(question.id.clone(), question)]);
+        let err = validate_questions(&questions, &Default::default()).unwrap_err();
+        assert!(err.to_string().contains("does not match any declared question id"));
+    }
+
+    #[test]
+    fn self_referencing_action_passes() {
+        let question: Question =
+            serde_yaml::from_str("id: /a\nname: A\nalternatives:\n  - name: Go\n    action: /a\n")
+                .unwrap();
+        let questions = std::collections::HashMap::from([(question.id.clone(), question)]);
+        assert!(validate_questions(&questions, &Default::default()).is_ok());
+    }
 }