fix(viewer,cli,export): clear the remaining 30 clippy lints

`cargo clippy --workspace -- -D warnings` now exits 0. `cargo test
--workspace` still reports 207 passed, 0 failed, 14 ignored across 30
suites — identical to runs 203 and 204, so none of this changed behaviour.

The workspace total was 73, not the 48 run 204 reported. `-D warnings`
turns a lint into a hard compile error, so `sylpheed-formats` failing
stopped its dependents from ever being built: `sylpheed-viewer` (14) and
`sylpheed-cli` (11) had never been linted by anyone. Clearing formats in
5c35a34 is what made them visible.

  formats  43 -> 0   (5c35a34)
  viewer   14 -> 0
  cli      11 -> 0
  export    5 -> 0

Collision surface, measured rather than assumed. Every viewer file
carrying a lint is byte-identical on both `auto/frame-blend-draw-path`
(495 commits) and `auto/port-p6-audio` (366). All eleven cli sites fall
outside every hunk either branch touches. 68 of the 73 sites could not
collide with anything.

The five that can are all in `sylpheed-export`, and three of those are
real:

  main.rs:278   `&out` -> `out`, inside frame-blend's hunk -278,12
  main.rs:318   `&out` -> `out`, inside port-p6-audio's hunk -303,44
  audio.rs:113  an added `#[allow]` in a file frame-blend DELETES

Each is one line. Resolving the first two means taking the branch's
version and re-applying a borrow removal; the third resolves to the
deletion. Flagged here so neither branch owner meets them cold.

Judgement calls, all stated at the site rather than suppressed globally:

* Three `too_many_arguments` in the viewer are false positives.
  `draw_viewer_ui`, `poll_loader_channel` and `apply_pak` are Bevy
  systems — every parameter is a `Res`/`ResMut`/`EventWriter` the
  scheduler injects, so the count is the framework's dependency list and
  cannot be reduced without a `SystemParam` struct.
* `cmd_screen_render` (cli, 8/7) is a plain function, so that one is real
  if mild; its arguments are the subcommand's flags.
* Two `dead_code` fields in export are serde schema fields. They model
  what the on-disc JSON accepts; deleting them would quietly change that.
* `iso_loader.rs` gains a `FrameRx` alias for the ffmpeg frame channel,
  which is what "very complex type" was asking for.

A site-local `#[allow]` with a reason is a decision recorded where it
applies: one lint, one function, and any new violation elsewhere still
fails the build. That is not the shape PROTOCOL.md forbids.

Closes #13

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01McNbzUeq1KRBWs4G6X2YVj

crates/sylpheed-export/src/audio.rs

@@ -109,6 +109,8 @@ pub struct BgmSpec {
     pub loop_start_s: Option<f64>,
     #[serde(default)]
     pub loop_end_s: Option<f64>,
+    // Deserialised to model the sidecar schema, not read in Rust.
+    #[allow(dead_code)]
     #[serde(default)]
     pub loop_end_why: Option<serde_json::Value>,
     #[serde(default)]

crates/sylpheed-export/src/main.rs

@@ -158,6 +158,9 @@ fn load_names(authored: &Path) -> Result<NameMap> {
     #[derive(serde::Deserialize)]
     struct File {
         archives: NameMap,
+        // Deserialised to model the on-disc schema, not read in Rust.
+        // Removing it would silently change what this struct accepts.
+        #[allow(dead_code)]
         #[serde(default)]
         also_export: AlsoExport,
     }
@@ -275,7 +278,7 @@ fn run_export(disc: &Path, out: &Path, authored_dir: &Path) -> Result<()> {
     // `video/` that this run did not claim, so a movie that stops being exported
     // still stops existing.
     if out.exists() {
-        for entry in std::fs::read_dir(&out).context("clear the output tree")? {
+        for entry in std::fs::read_dir(out).context("clear the output tree")? {
             let entry = entry?;
             if entry.file_name() == "video" {
                 continue;
@@ -288,7 +291,7 @@ fn run_export(disc: &Path, out: &Path, authored_dir: &Path) -> Result<()> {
             .with_context(|| format!("clear {}", entry.path().display()))?;
         }
     }
-    std::fs::create_dir_all(&out)?;
+    std::fs::create_dir_all(out)?;
 
     let archive = "dat/GP_TITLE.pak";
     let pak = disc.join(archive);
@@ -315,7 +318,7 @@ fn run_export(disc: &Path, out: &Path, authored_dir: &Path) -> Result<()> {
             None => (format!("build_{entry:02}"), "index", None),
         };
         let ex = screen::export_build(
-            &out,
+            out,
             archive,
             *entry,
             build_idx,