refactor(studio): 回放引擎改名 ReplayEngine —— 把「引擎」与「窗口级控制器」的名字分开

- What: `apps/studio/src/orisys_studio/replay.py` 的 `ReplayController` 改名为 `ReplayEngine`
  （引用只有 4 处：`app_window.py` 的 import 与构造、`ui_check.py` 的一处 import、模块内定义）；
  模块 docstring 写明它为什么叫 engine（只回答"t 时刻是什么"，不知道传输策略、不知道控件），
  并指路即将落地的窗口级 `ReplayController`；`app_window.replay` 这个属性名**不动**（36 处使用）。
  同步更新两份既有文档里的类名（`apps/studio/docs/shell-lifecycle.md`、`record-channel.md`、
  `docs/architecture/studio-architecture.md` 的框图标签）。
- Why: 用户已同意分拆 `app_window.py`，并选定"引擎改名 ReplayEngine + 新类叫 ReplayController"
  这一方案（另一方案是让两个名字 `ReplayController`/`ReplayCoordinator` 并存，容易进错门）。
  这一步是后续把窗口里那 30 个回放方法搬进 `ReplayController` 的前提：先把名字腾出来，
  否则搬迁时无法区分"引擎"与"控制器"。
- Verification: shared+apps 同一次运行 **588 项 0 失败 15 跳过**；`ui_check` 587 项 0 失败；
  全仓 `grep ReplayController` 只剩两处有意保留的提及（`replay.py` docstring 里指路、
  `app_window.py` 注释里指路），没有悬空引用。
- Not in this change: 不搬运任何方法、不改行为——`app_window.py` 仍是 3043 行；`SessionController`、
  `ReplayController`、`ViewLayoutController`、`DisplayPrefsController` 四个模块的搬迁尚未开始
  （顺序与契约见 docs/architecture/studio-architecture.md 建议 1）。

apps/studio/src/orisys_studio/app_window.py

@@ -48,7 +48,7 @@ from orisys_app_shared.paths import recordings_dir
 from orisys_app_shared.record import RecordConfig
 from orisys_app_shared.record.sample import to_record_sample
 from orisys_studio.recording import RecordingCoordinator, record_config_from_prefs
-from orisys_studio.replay import ReplayController
+from orisys_studio.replay import ReplayEngine
 from orisys_studio.scene3d.prefs import settings_to_prefs
 from orisys_app_shared.i18n import set_locale, t
 from orisys_app_shared.logging import report_error
@@ -190,8 +190,10 @@ class StudioMainWindow(QMainWindow):
         self._run_source_label = ""
         # ---- replay ---------------------------------------------------------
         # One engine for the history view: the recording reader, the cursor and
-        # the asynchronous depth recomputation. It renders nothing itself.
-        self.replay = ReplayController(self)
+        # the asynchronous depth recomputation. It renders nothing itself; the
+        # transport policy around it will move into a ReplayController (see
+        # docs/architecture/studio-architecture.md, suggestion 1).
+        self.replay = ReplayEngine(self)
         # ---- record channel -------------------------------------------------
         # Fed from the acquisition thread via the worker's sink list, so it does
         # not depend on the UI refresh rate or on which panels are visible.

apps/studio/src/orisys_studio/replay.py

@@ -6,6 +6,12 @@ panel, the curves read the recording through
 :class:`~orisys_app_shared.force.source.RecordingCurveSource`, and the transport
 on the chart header drives :meth:`set_position`.
 
+It is an *engine*, not a controller: it answers "what is at t?" and knows nothing about
+the transport's policy (when to start, what the end of the timeline means, whether a
+recompute pass is running) or about the widgets. That policy lives in
+``ReplayController`` (the window-level controller for this view), which is why the two
+names are deliberately different — see ``apps/studio/docs/shell-lifecycle.md``.
+
 There is no depth recomputation here: depth is not stored with a recording, the
 replay view shows the recorded frames, and re-running the pipeline over a video
 is the acquisition path's job (see the studio's "recompute" mode).
@@ -37,7 +43,7 @@ def _sdk_version() -> str:
         return ""
 
 
-class ReplayController(QObject):
+class ReplayEngine(QObject):
     """Open one recording and answer "what is at t?" for every view."""
 
     #: The cursor moved; the chart cursor and the 2D panel follow.