style: format the whole tree with cargo fmt (stock defaults, #35)

One-time, mechanical reformat — no functional changes. The tree was not
rustfmt-clean (~1800 hunks across ~100 files); this brings it to stock
`cargo fmt` defaults so a `cargo fmt --check` CI gate can follow.
Behaviour-preserving: 2509 pass / 0 fail / 1 ignored (unchanged baseline),
clippy clean. A .git-blame-ignore-revs entry follows so `git blame`
skips this commit.

tests/it/show_list.rs

@@ -17,7 +17,7 @@ use rdbms_playground::action::Action;
 use rdbms_playground::app::App;
 use rdbms_playground::db::Database;
 use rdbms_playground::dsl::{
-    parse_command, ColumnSpec, Command, ReferentialAction, ShowListKind, Type,
+    ColumnSpec, Command, ReferentialAction, ShowListKind, Type, parse_command,
 };
 use rdbms_playground::event::AppEvent;
 use rdbms_playground::mode::Mode;
@@ -108,8 +108,7 @@ fn rt() -> tokio::runtime::Runtime {
 
 fn open_project_db() -> (project::Project, Database, tempfile::TempDir) {
     let dir = tempfile::tempdir().expect("create tempdir");
-    let project =
-        project::open_or_create(None, Some(dir.path())).expect("open or create project");
+    let project = project::open_or_create(None, Some(dir.path())).expect("open or create project");
     let persistence = Persistence::new(project.path().to_path_buf());
     let db = Database::open_with_persistence(project.db_path(), persistence)
         .expect("open db with persistence");
@@ -195,8 +194,7 @@ fn show_relationships_lists_name_endpoints_and_nondefault_action() {
     // Name, both endpoints, and the non-default ON DELETE CASCADE
     // (ON UPDATE NO ACTION is the default and is omitted).
     assert_eq!(
-        lines[1],
-        "  orders_customer: Customers.id → Orders.customer_id on delete cascade",
+        lines[1], "  orders_customer: Customers.id → Orders.customer_id on delete cascade",
         "relationship summary line: {lines:?}",
     );
 }
@@ -222,7 +220,8 @@ fn show_lists_report_empty_collections_with_friendly_lines() {
     let rt = rt();
     // No schema seeded — every kind is empty.
     assert_eq!(
-        rt.block_on(db.show_list(ShowListKind::Tables, None)).unwrap(),
+        rt.block_on(db.show_list(ShowListKind::Tables, None))
+            .unwrap(),
         vec!["No tables in this project yet.".to_string()],
     );
     assert_eq!(
@@ -231,7 +230,8 @@ fn show_lists_report_empty_collections_with_friendly_lines() {
         vec!["No relationships in this project yet.".to_string()],
     );
     assert_eq!(
-        rt.block_on(db.show_list(ShowListKind::Indexes, None)).unwrap(),
+        rt.block_on(db.show_list(ShowListKind::Indexes, None))
+            .unwrap(),
         vec!["No indexes in this project yet.".to_string()],
     );
 }
@@ -246,7 +246,10 @@ fn show_one_relationship_renders_detail_block() {
     let rt = rt();
     rt.block_on(seed_schema(&db));
     let lines = rt
-        .block_on(db.show_list(ShowListKind::Relationships, Some("orders_customer".to_string())))
+        .block_on(db.show_list(
+            ShowListKind::Relationships,
+            Some("orders_customer".to_string()),
+        ))
         .expect("show relationship");
     assert_eq!(lines[0], "Relationship `orders_customer`:");
     assert_eq!(lines[1], "  Customers.id → Orders.customer_id");
@@ -262,7 +265,10 @@ fn show_one_index_renders_detail_block() {
     let rt = rt();
     rt.block_on(seed_schema(&db));
     let lines = rt
-        .block_on(db.show_list(ShowListKind::Indexes, Some("idx_orders_customer".to_string())))
+        .block_on(db.show_list(
+            ShowListKind::Indexes,
+            Some("idx_orders_customer".to_string()),
+        ))
         .expect("show index");
     assert_eq!(lines[0], "Index `idx_orders_customer` on Orders:");
     assert!(
@@ -329,7 +335,10 @@ fn app_show_tables_dispatches_show_list_command() {
             }
         )
     });
-    assert!(dispatched, "submit dispatches ShowList(Tables): {actions:?}");
+    assert!(
+        dispatched,
+        "submit dispatches ShowList(Tables): {actions:?}"
+    );
 }
 
 #[test]
@@ -337,10 +346,11 @@ fn app_renders_show_list_lines_as_system_output() {
     // Feed the success event directly so the test stays
     // self-contained (the worker round-trip is covered above).
     let mut app = App::new();
-    app.output.push_back(rdbms_playground::app::OutputLine::echo(
-        "show tables",
-        Mode::Simple,
-    ));
+    app.output
+        .push_back(rdbms_playground::app::OutputLine::echo(
+            "show tables",
+            Mode::Simple,
+        ));
     app.update(AppEvent::DslShowListSucceeded {
         command: Command::ShowList {
             kind: ShowListKind::Tables,
@@ -403,10 +413,11 @@ fn app_renders_show_relationship_as_a_styled_diagram() {
         .expect("found");
 
     let mut app = App::new();
-    app.output.push_back(rdbms_playground::app::OutputLine::echo(
-        "show relationship orders_customer",
-        Mode::Simple,
-    ));
+    app.output
+        .push_back(rdbms_playground::app::OutputLine::echo(
+            "show relationship orders_customer",
+            Mode::Simple,
+        ));
     app.update(AppEvent::DslShowRelationshipSucceeded {
         command: Command::ShowList {
             kind: ShowListKind::Relationships,
@@ -423,7 +434,10 @@ fn app_renders_show_relationship_as_a_styled_diagram() {
     // Both tables, box-drawing, the connector arrow, the actions line.
     assert!(text.contains("Orders"), "child box: {text}");
     assert!(text.contains("Customers"), "parent box: {text}");
-    assert!(text.contains('┌') && text.contains('│'), "box drawing: {text}");
+    assert!(
+        text.contains('┌') && text.contains('│'),
+        "box drawing: {text}"
+    );
     assert!(text.contains('▶'), "connector arrow: {text}");
     assert!(text.contains("on delete cascade"), "actions: {text}");
     // The diagram lines are styled (per-span runs), not plain system.
@@ -436,10 +450,11 @@ fn app_renders_show_relationship_as_a_styled_diagram() {
 #[test]
 fn app_show_relationship_not_found_shows_friendly_line() {
     let mut app = App::new();
-    app.output.push_back(rdbms_playground::app::OutputLine::echo(
-        "show relationship nope",
-        Mode::Simple,
-    ));
+    app.output
+        .push_back(rdbms_playground::app::OutputLine::echo(
+            "show relationship nope",
+            Mode::Simple,
+        ));
     app.update(AppEvent::DslShowRelationshipSucceeded {
         command: Command::ShowList {
             kind: ShowListKind::Relationships,
@@ -466,10 +481,11 @@ fn app_show_table_renders_relationships_as_compact_diagrams() {
         .expect("describe Orders");
 
     let mut app = App::new();
-    app.output.push_back(rdbms_playground::app::OutputLine::echo(
-        "show table Orders",
-        Mode::Simple,
-    ));
+    app.output
+        .push_back(rdbms_playground::app::OutputLine::echo(
+            "show table Orders",
+            Mode::Simple,
+        ));
     app.update(AppEvent::DslSucceeded {
         command: Command::ShowTable {
             name: "Orders".to_string(),