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/iteration4b_lifecycle_commands.rs

@@ -16,9 +16,9 @@ use rdbms_playground::app::{
     App, LoadPickerEntry, LoadPickerModal, LoadPickerSubMode, Modal, PathEntryModal,
     PathEntryPurpose,
 };
-use rdbms_playground::event::AppEvent;
 use rdbms_playground::db::Database;
 use rdbms_playground::dsl::{ColumnSpec, Type};
+use rdbms_playground::event::AppEvent;
 use rdbms_playground::persistence::Persistence;
 use rdbms_playground::project::{
     self, Project, ProjectKind, copy_project, safely_delete_temp_project,
@@ -462,11 +462,8 @@ fn temp_with_a_table_is_no_longer_unmodified() {
     let data = tempdir();
     let project = project::open_or_create(None, Some(data.path())).unwrap();
     let path = project.path().to_path_buf();
-    let db = Database::open_with_persistence(
-        project.db_path(),
-        Persistence::new(path.clone()),
-    )
-    .unwrap();
+    let db =
+        Database::open_with_persistence(project.db_path(), Persistence::new(path.clone())).unwrap();
     let rt = tokio::runtime::Builder::new_current_thread()
         .enable_all()
         .build()