style: apply cargo fmt across the crate (A20)

The repo never enforced rustfmt, so formatting had drifted broadly. This is a
single mechanical `cargo fmt` pass over the whole crate (no behavioral change;
lib suite green, 493 passed). Going forward fmt should be enforced (planned CI
fmt --check step). Part of the 0.6.1 hygiene pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/files.rs

@@ -76,10 +76,7 @@ pub fn sanitize_filename(raw: &str) -> String {
         .trim();
 
     // Drop control chars; turn other whitespace into single spaces later.
-    let cleaned: String = base
-        .chars()
-        .filter(|c| !c.is_control())
-        .collect();
+    let cleaned: String = base.chars().filter(|c| !c.is_control()).collect();
     let collapsed = cleaned.split_whitespace().collect::<Vec<_>>().join(" ");
     let collapsed = collapsed.trim_matches('.').trim();
 
@@ -145,7 +142,10 @@ pub fn looks_like_audio_name(name: &str) -> bool {
     let Some((_, extension)) = name.rsplit_once('.') else {
         return false;
     };
-    matches!(extension.to_ascii_lowercase().as_str(), "wav" | "mp3" | "ogg" | "oga" | "flac")
+    matches!(
+        extension.to_ascii_lowercase().as_str(),
+        "wav" | "mp3" | "ogg" | "oga" | "flac"
+    )
 }
 
 /// The attachment kind for some file bytes: [`AttachmentKind::Image`] if it
@@ -240,7 +240,11 @@ mod tests {
         let long_stem = "x".repeat(200);
         let name = format!("{long_stem}.png");
         let out = sanitize_filename(&name);
-        assert!(out.chars().count() <= MAX_FILENAME_LEN, "len was {}", out.chars().count());
+        assert!(
+            out.chars().count() <= MAX_FILENAME_LEN,
+            "len was {}",
+            out.chars().count()
+        );
         assert!(out.ends_with(".png"), "extension preserved: {out}");
     }
 
@@ -254,7 +258,9 @@ mod tests {
 
     #[test]
     fn image_sniffing_recognizes_containers() {
-        assert!(is_probably_image(&[0x89, b'P', b'N', b'G', 0x0D, 0x0A, 0x1A, 0x0A, 0, 0]));
+        assert!(is_probably_image(&[
+            0x89, b'P', b'N', b'G', 0x0D, 0x0A, 0x1A, 0x0A, 0, 0
+        ]));
         assert!(is_probably_image(&[0xFF, 0xD8, 0xFF, 0xE0]));
         assert!(is_probably_image(b"GIF89a...."));
         let mut webp = b"RIFF".to_vec();