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.

src/project/mod.rs

@@ -78,10 +78,7 @@ pub fn read_last_project(data_root: &Path) -> std::io::Result<Option<PathBuf>> {
 /// a moved/deleted directory is the kind of error `--resume`
 /// is supposed to surface clearly, not paper over by
 /// resolving symlinks at write time.
-pub fn write_last_project(
-    data_root: &Path,
-    project_path: &Path,
-) -> std::io::Result<()> {
+pub fn write_last_project(data_root: &Path, project_path: &Path) -> std::io::Result<()> {
     fs::create_dir_all(data_root)?;
     let final_path = data_root.join(LAST_PROJECT_FILE);
     let tmp_path = data_root.join(format!("{LAST_PROJECT_FILE}.tmp"));
@@ -108,9 +105,8 @@ pub fn resolve_data_root(override_dir: Option<&Path>) -> Result<PathBuf, Project
     if let Some(p) = override_dir {
         return Ok(p.to_path_buf());
     }
-    let dirs = ProjectDirs::from("", "", "rdbms-playground").ok_or(
-        ProjectError::DataRootUnavailable,
-    )?;
+    let dirs =
+        ProjectDirs::from("", "", "rdbms-playground").ok_or(ProjectError::DataRootUnavailable)?;
     Ok(dirs.data_dir().to_path_buf())
 }
 
@@ -255,21 +251,16 @@ pub enum ProjectError {
 impl std::fmt::Display for ProjectError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Self::DataRootUnavailable => {
-                f.write_str(&crate::t!("project.data_root_unavailable"))
+            Self::DataRootUnavailable => f.write_str(&crate::t!("project.data_root_unavailable")),
+            Self::PathNotFound(p) => {
+                f.write_str(&crate::t!("project.path_not_found", path = p.display(),))
+            }
+            Self::NotAProject(p) => {
+                f.write_str(&crate::t!("project.not_a_project", path = p.display(),))
+            }
+            Self::AlreadyExists(p) => {
+                f.write_str(&crate::t!("project.already_exists", path = p.display(),))
             }
-            Self::PathNotFound(p) => f.write_str(&crate::t!(
-                "project.path_not_found",
-                path = p.display(),
-            )),
-            Self::NotAProject(p) => f.write_str(&crate::t!(
-                "project.not_a_project",
-                path = p.display(),
-            )),
-            Self::AlreadyExists(p) => f.write_str(&crate::t!(
-                "project.already_exists",
-                path = p.display(),
-            )),
             Self::Io { path, source } => f.write_str(&crate::t!(
                 "project.io",
                 path = path.display(),
@@ -609,11 +600,10 @@ pub fn safely_delete_temp_project(
     // 2. Canonicalize for the containment check. We do this
     //    only after the symlink-at-top check so we can't be
     //    tricked by a top-level symlink.
-    let project_canon =
-        fs::canonicalize(project_path).map_err(|source| SafeDeleteError::Io {
-            path: project_path.to_path_buf(),
-            source,
-        })?;
+    let project_canon = fs::canonicalize(project_path).map_err(|source| SafeDeleteError::Io {
+        path: project_path.to_path_buf(),
+        source,
+    })?;
 
     // 3. Containment: canonical path must be inside the
     //    canonical data-root projects dir.
@@ -848,7 +838,10 @@ mod tests {
         assert!(gi.contains("/playground.db"));
         assert!(gi.contains("/.rdbms-playground.lock"));
         assert!(gi.contains("/.snapshots/"), "undo ring should be ignored");
-        assert!(!gi.contains("history.log"), "history.log should NOT be ignored");
+        assert!(
+            !gi.contains("history.log"),
+            "history.log should NOT be ignored"
+        );
     }
 
     #[test]
@@ -890,7 +883,10 @@ mod tests {
         let target = tmp.path().join("MyProject");
         fs::create_dir(&target).unwrap();
         let err = Project::create_named(&target).expect_err("must refuse");
-        assert!(matches!(err, ProjectError::AlreadyExists(_)), "got: {err:?}");
+        assert!(
+            matches!(err, ProjectError::AlreadyExists(_)),
+            "got: {err:?}"
+        );
     }
 
     #[test]
@@ -962,7 +958,10 @@ mod tests {
         )
         .unwrap();
         let read_back = read_last_project(tmp.path()).unwrap();
-        assert_eq!(read_back, Some(std::path::PathBuf::from("/tmp/some/project")));
+        assert_eq!(
+            read_back,
+            Some(std::path::PathBuf::from("/tmp/some/project"))
+        );
     }
 
     #[test]