app: migrate playhead/undo/modified events off EventBridge (issues 5-8)

- issue 5 (#53): ExportDialog playhead via PlaybackController
- issue 6 (#54): timebasedwidget/timelinewidget playhead via PlaybackController
- issue 7 (#55): historywidget via app-internal Core::undo_index_changed
- issue 8 (#33): PROJECT_MODIFIED_CHANGED re-broadcast as Core::project_modified_changed

docs/plans/eliminate-event-bridge-issues.md

@@ -106,13 +106,13 @@ In other words: one app-side controller that every
 - Acceptance: the value tree refreshes with the playhead.
 - **Required: build + ctest all green.**
 
-### issue 5 — ExportDialog playhead
+### issue 5 ✅ (done) — ExportDialog playhead
 `app/dialog/export/export.cpp:311` (raw C).
 - Acceptance: the export dialog's in/out times stay in sync with the
   playhead.
 - **Required: build + ctest all green.**
 
-### issue 6 — timelinewidget / viewerdisplay playhead family (bridge subscriptions)
+### issue 6 ✅ (done) — timelinewidget / viewerdisplay playhead family (bridge subscriptions)
 `app/widget/timelinewidget/timelinewidget.cpp` (around :741-743) and the
 related viewerdisplay subscriptions. Reconnect to PlaybackController.
 - Acceptance: timeline timecode/playhead position display correctly.
@@ -122,7 +122,7 @@ related viewerdisplay subscriptions. Reconnect to PlaybackController.
 
 ## Undo & modified migrations (pattern A, about half a day each)
 
-### issue 7 — historywidget UNDO_INDEX_CHANGED
+### issue 7 ✅ (done) — historywidget UNDO_INDEX_CHANGED
 `app/widget/history/historywidget.cpp:33,127` (two raw C callbacks).
 Emit an app-internal `undo_index_changed(int)` at Core's undo/redo/push
 exit points and reconnect historywidget to it.
@@ -130,7 +130,7 @@ exit points and reconnect historywidget to it.
   the correct row.
 - **Required: build + ctest all green.**
 
-### issue 8 — core.cpp PROJECT_MODIFIED_CHANGED
+### issue 8 ✅ (done) — core.cpp PROJECT_MODIFIED_CHANGED
 `app/core.cpp:1108` (raw C). The modified flag is driven by the undo stack,
 so the app can derive it at push/undo/redo/load; drive `setWindowModified`
 from an app-internal signal instead.

docs/zh/plans/eliminate-event-bridge-issues.md

@@ -104,12 +104,12 @@ PlaybackController::playhead_changed。
 - 验收 / Acceptance：值树随播放头刷新。
 - **必做 / Required：build + ctest 全绿。**
 
-### issue 5 — ExportDialog playhead
+### issue 5 ✅ (done) — ExportDialog playhead
 `app/dialog/export/export.cpp:311`（裸 C）。
 - 验收 / Acceptance：导出对话框 in/out 时间随播放头同步。
 - **必做 / Required：build + ctest 全绿。**
 
-### issue 6 — timelinewidget / viewerdisplay 的 playhead 族（bridge 订阅）
+### issue 6 ✅ (done) — timelinewidget / viewerdisplay 的 playhead 族（bridge 订阅）
 `app/widget/timelinewidget/timelinewidget.cpp`（:741-743 一带）与 viewerdisplay
 的相关订阅。改连 PlaybackController。
 - 验收 / Acceptance：时间线时间码/播放头位置显示正确。
@@ -119,14 +119,14 @@ PlaybackController::playhead_changed。
 
 ## undo/modified 族迁移 / Undo & modified migrations（模式 A，约半天/个）
 
-### issue 7 — historywidget 的 UNDO_INDEX_CHANGED
+### issue 7 ✅ (done) — historywidget 的 UNDO_INDEX_CHANGED
 `app/widget/history/historywidget.cpp:33,127`（裸 C 两处）。
 在 Core 的 undo/redo/push 出口 emit app 内 `undo_index_changed(int)`，
 historywidget 改连它。
 - 验收 / Acceptance：undo/redo 后历史列表 model reset 且选中行正确。
 - **必做 / Required：build + ctest 全绿。**
 
-### issue 8 — core.cpp 的 PROJECT_MODIFIED_CHANGED
+### issue 8 ✅ (done) — core.cpp 的 PROJECT_MODIFIED_CHANGED
 `app/core.cpp:1108`（裸 C）。modified 由 undo 栈驱动，app 在
 push/undo/redo/load 处即可推导；改为 app 内信号驱动 `setWindowModified`。
 - 验收 / Acceptance：编辑/撤销/保存后标题栏修改标记正确。