M11: Optimize PDF and Reduce File Size run in the background with a progress bar (#370)

* M11: Optimize PDF and Reduce File Size run in the background with a progress bar

Advanced optimization and Reduce File Size did all their work on the UI
thread, so on a large file the window stopped repainting until they were
done and looked as if it had crashed.

- pdfcraft-optimize: optimize_with_progress reports each image and the
  clean-up; returning false stops with OptimizeError::Cancelled.
- engine: Session::optimize_job captures a copy of the document and the
  choices; OptimizeJob::run reports each OptimizeStage (removing user data,
  images, cleaning up, merging, writing), stops on request with
  EditError::Cancelled and turns a panic into an error so a worker always
  reports back. optimized_bytes is the job run in place.
- ui: both commands run the job on a worker thread (inline in tests and on
  the web), like OCR and Export. A card at the bottom centre shows the
  stage ("Optimizing... image 14 of 40"), a bar that eases towards the
  fraction with a light sweeping across it, the percentage and Cancel;
  notices stack above it. A second run is refused while one is going. The
  control channel's state includes the progress.

The headless doc_optimize and doc_reduce tools stay synchronous. New
strings are translated for es, fr, ja, zh-hans, zh-hant.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Clippy: as_chunks in the signature image background test (follow-up to #355)

#360 switched the image test to as_chunks; #355 added another chunks_exact(4)
in the background test, which clippy's chunks_exact_to_as_chunks rejects.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Optimize: report a failed worker spawn instead of waiting forever

Co-Authored-By: Claude Opus 5.5 <[email protected]>

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

crates/optimize/tests/optimize.rs

@@ -265,3 +265,42 @@ fn invalid_links_and_unreferenced_destinations_go() {
     let off = Settings { remove_invalid_links: false, remove_unreferenced_dests: false, ..Settings::default() };
     assert_eq!(optimize(&mut again, &off).unwrap().invalid_links, 0);
 }
+
+#[test]
+fn progress_is_reported_per_image_and_a_refusal_cancels() {
+    use pdfcraft_optimize::{OptimizeError, Stage, optimize_with_progress};
+    let build = || {
+        let mut doc = Document::new_empty();
+        let a = image(&mut doc, 300, 300, 3, false, None);
+        let b = image(&mut doc, 300, 300, 1, false, None);
+        let c = image(&mut doc, 300, 300, 3, true, None);
+        page(&mut doc, &[("A", a), ("B", b), ("C", c)], "q 72 0 0 72 0 0 cm /A Do Q q 72 0 0 72 100 0 cm /B Do Q q 72 0 0 72 200 0 cm /C Do Q");
+        doc
+    };
+    let mut seen = Vec::new();
+    let report = optimize_with_progress(&mut build(), &Settings::default(), &mut |s| {
+        seen.push(s);
+        true
+    })
+    .unwrap();
+    assert_eq!(report.images, 3);
+    assert_eq!(
+        seen,
+        [
+            Stage::Images { done: 0, total: 3 },
+            Stage::Images { done: 1, total: 3 },
+            Stage::Images { done: 2, total: 3 },
+            Stage::Images { done: 3, total: 3 },
+            Stage::CleanUp
+        ]
+    );
+
+    // Stopping after the first image.
+    let mut calls = 0;
+    let r = optimize_with_progress(&mut build(), &Settings::default(), &mut |_| {
+        calls += 1;
+        calls < 2
+    });
+    assert!(matches!(r, Err(OptimizeError::Cancelled)), "{r:?}");
+    assert_eq!(calls, 2, "nothing runs after the refusal");
+}