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 <noreply@anthropic.com>

* 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 <noreply@anthropic.com>

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

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

parity/acrobat-features.toml

@@ -7107,7 +7107,7 @@ status = "shipped"
 commands = ["optimize.reduce"]
 tools = ["doc_reduce"]
 evidence = ["crates/ui-egui/tests/create.rs::reduce_file_size_writes_a_compact_copy", "crates/engine/src/tests.rs::create_and_reduce", "crates/automation/tests/automation.rs::creating_and_reducing_through_tools", "crates/automation/tests/automation.rs::optimizing_through_tools"]
-notes = "images above 225 ppi to 150 ppi JPEG medium, thumbnails dropped, resources merged, object streams"
+notes = "images above 225 ppi to 150 ppi JPEG medium, thumbnails dropped, resources merged, object streams; runs in the background with a progress bar and Cancel"
 
 [[feature]]
 id = "optimize.compatibility-level"
@@ -7130,8 +7130,8 @@ milestone = "M11"
 status = "partial"
 commands = ["optimize.advanced"]
 tools = ["doc_optimize"]
-evidence = ["crates/ui-egui/tests/create.rs::the_pdf_optimizer_dialog_saves_an_optimized_copy", "crates/automation/tests/automation.rs::optimizing_through_tools"]
-notes = "Images, Discard Objects, Discard User Data, Clean Up; no Fonts or Transparency panels, no space audit"
+evidence = ["crates/ui-egui/tests/create.rs::the_pdf_optimizer_dialog_saves_an_optimized_copy", "crates/automation/tests/automation.rs::optimizing_through_tools", "crates/ui-egui/src/optimize_ui.rs::the_progress_card_shows_the_stage_and_cancels", "crates/engine/src/tests.rs::an_optimize_job_reports_its_stages_and_can_be_cancelled"]
+notes = "Images, Discard Objects, Discard User Data, Clean Up; runs in the background with a progress bar (per image) and Cancel; no Fonts or Transparency panels, no space audit"
 
 [[feature]]
 id = "optimize.downsample-images"