Phase 3 (Organize + robust save) + Phase 4 (Edit content); update docs

Engine:
- organize.rs: build_document(plan) core — insert/delete/rotate/crop/extract/merge/split
- watermark.rs: watermark + header/footer via PdfPages::watermark, CID Unicode fonts
- qpdf.rs: QPDF CLI wrapper — repair corrupt files, re-encrypt after edits, ensure_openable
- edit.rs: MOAT — list_objects + apply_edits (SetText VN, Transform, Delete, Add/ReplaceImage)
- Tests: organize/watermark/qpdf_safety/edit roundtrip — 43/43 engine tests green

UI (Tauri): "Tổ chức trang" mode (grid + drag-reorder + multi-select), "Sửa nội dung"
mode (WYSIWYG object overlay, edit-in-place), global undo/redo, robust file open.

Corpus: add encrypted.pdf + corrupt-truncated.pdf fixtures.

Docs: mark Phase 1-4 done in roadmap; document QPDF setup + engine module layout in
05-dev-setup; add 10-13 phase summaries & user-test checklists; README status.

docs/05-dev-setup.md

@@ -7,6 +7,7 @@
 - **Visual Studio Build Tools** + workload **Desktop development with C++** (cung cấp `cl.exe`/`link.exe` cho linker MSVC).
 - **WebView2 Runtime** (cho Tauri; Windows 11 thường có sẵn).
 - **PDFium**: `pdfium.dll` prebuilt — tải bằng `scripts/fetch-pdfium.ps1` (đặt vào gốc workspace + `pdfium/`).
+- **QPDF** (từ Phase 3): `qpdf.exe` prebuilt — tải bằng `scripts/fetch-qpdf.ps1`. Dùng để sửa file hỏng (repair) trước khi PDFium mở + mã hoá lại file sau khi chỉnh sửa.
 - (Tauri) Node không bắt buộc: app dùng frontend tĩnh, chạy thẳng bằng `cargo run`.
 
 ## Lấy PDFium
@@ -16,16 +17,29 @@ powershell -File scripts/fetch-pdfium.ps1
 ```
 Engine tìm `pdfium.dll` theo thứ tự: `FOFREEXIT_PDFIUM_PATH` → cwd → `./pdfium` → thư mục exe → thư viện hệ thống.
 
+## Lấy QPDF
+```powershell
+# Tải qpdf.exe (prebuilt) về workspace
+powershell -File scripts/fetch-qpdf.ps1
+```
+Engine tìm `qpdf.exe` theo thứ tự: `FOFREEXIT_QPDF_PATH` → `<cwd>/qpdf/bin/qpdf.exe` → cạnh file exe → `qpdf` trong PATH hệ thống (xem `crates/ff-engine/src/qpdf.rs`).
+
 ## Cấu trúc
 ```
 crates/ff-cos        # COS layer (khung)
 crates/ff-pdmodel    # PD layer (khung)
-crates/ff-engine     # render qua PDFium (Phase 1: render.rs)
-crates/ff-cli        # CLI "ff" (info, render)
+crates/ff-engine     # render + chỉnh sửa qua PDFium/QPDF
+  render.rs          #   Phase 1: render trang, page_dims, extract_text, search, outline
+  annot.rs           #   Phase 2: chú thích (highlight/note/shape/free-draw...)
+  organize.rs        #   Phase 3: tổ chức trang (insert/delete/rotate/crop/merge/split)
+  watermark.rs       #   Phase 3: watermark + header/footer
+  qpdf.rs            #   Phase 3: repair file hỏng + mã hoá lại (QPDF CLI)
+  edit.rs            #   Phase 4: sửa nội dung (text run/object) trực tiếp
+crates/ff-cli        # CLI "ff" (info, render, pages, text, search, outline)
 app/src              # frontend tĩnh (HTML/CSS/JS)
 app/src-tauri        # backend Tauri (crate riêng, workspace tách)
 corpus/              # PDF mẫu để test
-scripts/             # tiện ích (fetch-pdfium)
+scripts/             # tiện ích (fetch-pdfium, fetch-qpdf)
 ```
 
 ## CLI
@@ -46,8 +60,10 @@ cargo run -p ff-cli -- outline corpus\sample-multipage.pdf
 
 ## Test
 ```powershell
-cargo test -p ff-engine          # smoke test render (cần pdfium.dll)
+cargo test -p ff-engine          # toàn bộ test engine (cần pdfium.dll + qpdf.exe)
 ```
+Bao gồm: render smoke, viewer features, big-doc, annot round-trip (Phase 1–2),
+organize/watermark/qpdf-safety (Phase 3), edit round-trip (Phase 4). Hiện **43/43 xanh**.
 
 ## Chạy app desktop (Tauri)
 ```powershell