fix(hint): labelled tier-3 block format + snapshot (ADR-0053 /runda)

Final /runda found the rendered block was three bare unlabelled lines,
deviating from the approved exemplar format. Fix:
- emit_tier3_block now renders a `Hint` heading + aligned `What:` /
  `Example:` / `Concept:` lines (hint.block.* labels); concept stays muted
- lock the format with an insta snapshot (hint_block_insert)
- amend ADR-0053 D2/D4 + exemplars: drop the `Next:` line (tier-2 ambient
  already owns live position-awareness — user-confirmed), align exemplars
  to the shipped format

2499 pass / 1 ignored, clippy clean.

src/app.rs

@@ -3205,17 +3205,32 @@ impl App {
     /// polish (the framed block) lands with the corpus.
     fn emit_tier3_block(&mut self, stem: &str) -> bool {
         let cat = crate::friendly::catalog();
-        if cat.get(&format!("{stem}.what")).is_none() {
+        let what_key = format!("{stem}.what");
+        if cat.get(&what_key).is_none() {
             return false;
         }
-        self.note_system(crate::friendly::translate(&format!("{stem}.what"), &[]));
+        // Labelled block (ADR-0053 D4): a `Hint` heading, then aligned
+        // `What:` / `Example:` / `Concept:` lines. `concept` renders
+        // muted (`OutputStyleClass::Hint`); the rest are plain system.
+        let labelled = |label: &str, value: &str| {
+            // Pad `<Label>:` to a common width so the values align.
+            format!("  {:<9}{value}", format!("{label}:"))
+        };
+        self.note_system(crate::t!("hint.block.heading"));
+        self.note_system(labelled(
+            &crate::t!("hint.block.what"),
+            &crate::friendly::translate(&what_key, &[]),
+        ));
         if cat.get(&format!("{stem}.example")).is_some() {
-            self.note_system(crate::friendly::translate(&format!("{stem}.example"), &[]));
+            self.note_system(labelled(
+                &crate::t!("hint.block.example"),
+                &crate::friendly::translate(&format!("{stem}.example"), &[]),
+            ));
         }
         if cat.get(&format!("{stem}.concept")).is_some() {
-            self.push_category_three_prose(crate::friendly::translate(
-                &format!("{stem}.concept"),
-                &[],
+            self.push_category_three_prose(labelled(
+                &crate::t!("hint.block.concept"),
+                &crate::friendly::translate(&format!("{stem}.concept"), &[]),
             ));
         }
         true
@@ -5813,6 +5828,22 @@ mod tests {
         );
     }
 
+    /// Locks the rendered tier-3 block format (ADR-0053 D4): a `Hint`
+    /// heading + aligned `What:` / `Example:` / `Concept:` lines.
+    #[test]
+    fn insert_hint_block_renders_in_the_labelled_format() {
+        let mut app = App::new();
+        type_str(&mut app, "insert into Customers ");
+        f1(&mut app);
+        let block = app
+            .output
+            .iter()
+            .map(|l| l.text.as_str())
+            .collect::<Vec<_>>()
+            .join("\n");
+        insta::assert_snapshot!("hint_block_insert", block);
+    }
+
     #[test]
     fn f1_on_add_relationship_renders_the_relationship_block() {
         let mut app = App::new();