feat: V5 show tables / relationships / indexes list commands

Add the list-all show family as one Command::ShowList { kind }
variant. A read-only worker show_list formats count-headed lists
(reusing do_list_tables / read_all_relationships /
read_table_indexes, so it never drifts from the items panel);
internal __rdbms_* tables excluded. Help + parse-usage entries
added; 10 integration tests in tests/it/show_list.rs.

Mark V5 [x]. Split the singular show relationship/index <name>
detail forms (the [<name>] half) into a new tracked V5a [ ] item
rather than leaving them as an untracked footnote.

src/input_render.rs

@@ -2050,9 +2050,19 @@ mod tests {
     }
 
     #[test]
-    fn ambient_hint_at_word_boundary_after_show_returns_data_table() {
+    fn ambient_hint_at_word_boundary_after_show_returns_all_subcommands() {
+        // data / table plus the V5 list-all forms, grammar order.
         let cs = cands_hint("show ", 5).expect("candidate hint");
-        assert_eq!(cs, vec!["data".to_string(), "table".to_string()]);
+        assert_eq!(
+            cs,
+            vec![
+                "data".to_string(),
+                "table".to_string(),
+                "tables".to_string(),
+                "relationships".to_string(),
+                "indexes".to_string(),
+            ],
+        );
     }
 
     #[test]