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/friendly/format.rs

@@ -43,17 +43,11 @@ impl Catalog {
     }
 }
 
-fn flatten(
-    value: &serde_norway::Value,
-    prefix: String,
-    out: &mut HashMap<String, String>,
-) {
+fn flatten(value: &serde_norway::Value, prefix: String, out: &mut HashMap<String, String>) {
     match value {
         serde_norway::Value::Mapping(map) => {
             for (k, v) in map {
-                let k_str = k
-                    .as_str()
-                    .expect("catalog keys must be strings");
+                let k_str = k.as_str().expect("catalog keys must be strings");
                 let next = if prefix.is_empty() {
                     k_str.to_string()
                 } else {
@@ -85,9 +79,7 @@ pub fn catalog() -> &'static Catalog {
 /// See module docs for failure modes.
 pub fn translate(key: &str, args: &[(&str, &dyn Display)]) -> String {
     let template = catalog().get(key).unwrap_or_else(|| {
-        panic!(
-            "missing catalog key: `{key}` (the validator should have caught this)"
-        );
+        panic!("missing catalog key: `{key}` (the validator should have caught this)");
     });
     substitute(template, args, key)
 }