style: rustfmt sweep -- 774 hunks across 154 files -> 0

`cargo fmt --all -- --check` has failed on every run in this repository's
history, identically on `main` and on every branch. This is #12.

Mechanical: `cargo fmt --all`, nothing else. 154 files, all `.rs`, no other
extension touched. `cargo check --workspace` exits 0 afterwards, so nothing
changed semantically.

ON THE ORDERING, WHICH WAS THE REAL QUESTION.

HANDOFF-2026-09-06 section 7 warns this is the expensive fix: a whole-tree
reformat before #7 and #8 return "would put a conflict in every file of 861
commits and make the reviews those items exist to enable unreadable".

That is measurably too pessimistic, and it had been reasoned rather than
tested. Measured here by three-way merging a rustfmt'd `main` against both
unmerged branches, file by file:

  file/branch pairs tested   32
  merges CLEAN               28
  merges CONFLICTING          4   (8 conflict hunks total)

    sylpheed-cli/src/main.rs      1 hunk
    sylpheed-export/src/check.rs  1
    sylpheed-export/src/screen.rs 4
    sylpheed-export/src/video.rs  2

All four are against `auto/frame-blend-draw-path` only;
`auto/port-p6-audio` does not conflict anywhere. The earlier framing --
154 dirty files, 133 that cannot collide, 21 that can, the collision set
carrying 147 of 774 hunks (19%) -- reproduces exactly. What it did not say
is that most of the 21 still merge cleanly, because rustfmt's edits and the
branches' edits rarely land on the same lines.

So the cost of sweeping now is 4 files and 8 hunks for one branch, against
a check that is otherwise red forever. Deliberately NOT folded into the
WASM PR: 154 reformatted files would make that one unreviewable.

Closes #12

crates/sylpheed-formats/tests/ui_focus_kind_disc.rs

@@ -46,7 +46,9 @@ fn for_each_build(root: &Path, mut f: impl FnMut(&str, &[u8])) {
     paks.sort();
     for p in &paks {
         let name = p.file_name().unwrap().to_string_lossy().to_string();
-        let Ok(arc) = PakArchive::open(p) else { continue };
+        let Ok(arc) = PakArchive::open(p) else {
+            continue;
+        };
         for e in arc.entries() {
             let Ok(bytes) = arc.read(e) else { continue };
             if ratc::is_ratc(&bytes) {
@@ -146,7 +148,10 @@ fn focused_and_base_declaration_entries_are_compared_word_by_word() {
         eprintln!("  {e}");
     }
 
-    assert!(pairs > 0, "no focused/base pairs found — the sweep is broken");
+    assert!(
+        pairs > 0,
+        "no focused/base pairs found — the sweep is broken"
+    );
 
     // MEASURED 2026-08-24, and asserted so the answer cannot rot back into a
     // suspicion: all 54 pairs on the disc carry the SAME `kind`, no bit is ever
@@ -156,7 +161,10 @@ fn focused_and_base_declaration_entries_are_compared_word_by_word() {
     // focused state at all, and the naming pairing is not a shortcut around a
     // field that exists: there is no field.
     assert_eq!(pairs, 54, "the disc has 54 name-paired focused elements");
-    assert_eq!(kind_equal, pairs, "some pair's `kind` differs from its base");
+    assert_eq!(
+        kind_equal, pairs,
+        "some pair's `kind` differs from its base"
+    );
     assert!(
         set_on_focused.is_empty(),
         "a kind bit distinguishes focused from base: {set_on_focused:?}"