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/friendly/keys.rs

@@ -306,6 +306,9 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("parse.usage.select", &[]),
     ("parse.usage.show_data", &[]),
     ("parse.usage.show_table", &[]),
+    ("parse.usage.show_tables", &[]),
+    ("parse.usage.show_relationships", &[]),
+    ("parse.usage.show_indexes", &[]),
     ("parse.usage.update", &[]),
     ("parse.usage.with", &[]),
     ("parse.expect.select_projection", &[]),

src/friendly/strings/en-US.yaml

@@ -317,6 +317,9 @@ help:
     show: |-
         show table <T>             — show a table's structure
         show data <T>              — show a table's rows
+        show tables                — list all tables
+        show relationships         — list all relationships
+        show indexes               — list all indexes
     insert: |-
         insert into <T> [(cols)] [values] (vals)        — add a row
     update: |-
@@ -554,6 +557,9 @@ parse:
         [--force-conversion | --dont-convert]
     show_data: "show data <Table>"
     show_table: "show table <Table>"
+    show_tables: "show tables"
+    show_relationships: "show relationships"
+    show_indexes: "show indexes"
     insert: "insert into <Table> [(<col>[, ...])] [values] (<value>[, ...])"
     update: "update <Table> set <col>=<value>[, ...] (where <col>=<value> | --all-rows)"
     delete: "delete from <Table> (where <col>=<value> | --all-rows)"