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/dsl/command.rs

@@ -332,6 +332,13 @@ pub enum Command {
     ShowTable {
         name: String,
     },
+    /// Re-display a whole schema collection — every table,
+    /// relationship, or index — as a list in the output (V5). The
+    /// read-only "all items" sibling of `ShowTable`; pure display,
+    /// no schema change.
+    ShowList {
+        kind: ShowListKind,
+    },
     /// Insert a single row. `columns` is `None` for the natural-
     /// order short form (`insert into T values (...)`); the
     /// executor fills in the column list by walking the schema.
@@ -746,6 +753,36 @@ pub enum IndexSelector {
     Columns { table: String, columns: Vec<String> },
 }
 
+/// Which schema collection a `show <kind>` list command displays (V5).
+///
+/// The bare plural forms list every item of the kind across the
+/// project; the singular `show table <name>` (a separate
+/// `Command::ShowTable`) shows one. The singular `show
+/// relationship <name>` / `show index <name>` forms are not yet
+/// provided — only the list-all forms land here.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ShowListKind {
+    /// `show tables` — every user table (internal `__rdbms_*`
+    /// tables excluded, as in the items panel).
+    Tables,
+    /// `show relationships` — every declared FK relationship.
+    Relationships,
+    /// `show indexes` — every index across all tables.
+    Indexes,
+}
+
+impl ShowListKind {
+    /// The full command name for the `name()` / echo surface.
+    #[must_use]
+    pub const fn command_name(self) -> &'static str {
+        match self {
+            Self::Tables => "show tables",
+            Self::Relationships => "show relationships",
+            Self::Indexes => "show indexes",
+        }
+    }
+}
+
 /// The action of an advanced-mode `ALTER TABLE` (ADR-0035 §4).
 ///
 /// Sub-phase 4e carries the column actions; 4f adds `AlterColumnType`;
@@ -860,6 +897,7 @@ impl Command {
             Self::AddConstraint { .. } => "add constraint",
             Self::DropConstraint { .. } => "drop constraint",
             Self::ShowTable { .. } => "show table",
+            Self::ShowList { kind } => kind.command_name(),
             Self::Insert { .. } => "insert into",
             Self::Update { .. } => "update",
             Self::Delete { .. } => "delete from",
@@ -948,6 +986,10 @@ impl Command {
             // result renders as a data view, not a structure
             // view, so an empty target is correct here.
             Self::Select { .. } => "",
+            // A `show <kind>` list spans every table (or none) —
+            // there is no single structure-target table; it renders
+            // as a list, not a structure view.
+            Self::ShowList { .. } => "",
             // A SQL `INSERT` carries its parsed target table (for
             // CSV re-persistence and ok-summary subject).
             Self::SqlInsert { target_table, .. }