refactor: workspace layout — crates/, app at root, legacy C++ removed

Single mechanical restructure commit:
- root Cargo.toml = oakapp bin + workspace; one cargo build produces
  oakapp, oak-cli, oak-worker, liboakengine.dylib
- app/rust/src -> src/ (app at repo root, no rust/ nesting)
- src/<mod>/rust -> crates/oak<mod>; src/oakcore-rs -> crates/oakcore;
  src/bindings/oakotio -> crates/oakotio; src/engine/rust ->
  crates/oakengine (keeps cdylib+staticlib+rlib)
- public C headers include/<mod>/ -> crates/oakengine/include/<mod>/
- OFX SDK headers vendored into crates/oakplugin/ofx/ (HostSupport gone)
- legacy deleted: old src/ C++ modules, engine/, core/, ffmpeg_bridge/,
  app/ (Qt), cli/worker C++, root CMakeLists, third_party/KDDockWidgets
  submodule, otio-install, all build-* output (~40GB)
- oakstorage kept but excluded from the workspace (skeleton w/ todos);
  gpui excluded (own workspace)
- verified: cargo build green, cargo test --workspace 1845/0
  (with the documented OCIO_RS_* env override for the homebrew OCIO)

crates/oakplugin/src/progress.rs

@@ -0,0 +1,86 @@
+// Oak Video Editor - Non-Linear Video Editor
+// Copyright (C) 2026 Oak Team
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//! 进度上报（Progress suite 的宿主侧）。
+//!
+//! 对应 C++ 的 `PluginProgressReporter`。进度/取消经 facade 注册的
+//! 回调出 crate（M9 的 facade 回调模式，不设全局状态）。
+//! 取消是粘滞的：一旦回调答 false，本报告器的 [`is_cancelled`]
+//! （image effect suite 的 abort 查询）持续为真。
+
+use std::ffi::c_int;
+
+use std::sync::atomic::{AtomicBool, Ordering};
+
+/// 进度回调：签名与 `include/plugin/instance.h` 的
+/// `oakplugin_progress_fn` 逐字一致——`(progress, userdata)`，
+/// 返回非 0 表示应中止（骨架声明为 `(userdata, progress) -> bool`，
+/// 与头文件不符，以此为准）。
+pub type ProgressFn = unsafe extern "C" fn(progress: f64, userdata: *mut std::ffi::c_void) -> c_int;
+
+/// 进度上报器。render 路径持有一份，Progress suite 的
+/// progressStart/Update/End 转发到这里。
+pub struct ProgressReporter {
+	callback: Option<ProgressFn>,
+	userdata: usize,
+	/// 取消标志（粘滞；update 返回 false 时置位）。
+	cancelled: AtomicBool,
+}
+
+impl ProgressReporter {
+	/// 无回调（渲染静默进行）。
+	pub fn silent() -> Self {
+		Self {
+			callback: None,
+			userdata: 0,
+			cancelled: AtomicBool::new(false),
+		}
+	}
+
+	/// 带回调。
+	///
+	/// # Safety
+	/// `userdata` 的生命周期由注册方保证。
+	pub unsafe fn new(callback: ProgressFn, userdata: *mut std::ffi::c_void) -> Self {
+		Self {
+			callback: Some(callback),
+			// usize 存（裸指针破坏 Send 推导；值语义不变）。
+			userdata: userdata as usize,
+			cancelled: AtomicBool::new(false),
+		}
+	}
+
+	/// 报告进度；返回 false 表示应取消（映射
+	/// kOfxStatReplyNo/action 失败由调用点决定）。
+	pub fn update(&self, progress: f64) -> bool {
+		match self.callback {
+			Some(cb) => {
+				// 头文件契约：非 0 = 中止。
+				let abort = unsafe { cb(progress, self.userdata as *mut std::ffi::c_void) } != 0;
+				if abort {
+					self.cancelled.store(true, Ordering::Relaxed);
+				}
+				!abort
+			}
+			None => true,
+		}
+	}
+
+	/// 本次渲染是否已被取消（image effect suite 的 abort 透传）。
+	pub(crate) fn is_cancelled(&self) -> bool {
+		self.cancelled.load(Ordering::Relaxed)
+	}
+}