R5.6: ElyShow right-click menus, PowerPoint-style; Impress table borders drag; R3 PASS

The canvas offers Ely's menu by target: slide (layouts, comment), text
(bullets, numbering, comment), shape or text box, picture (replace,
crop), table (insert, delete, merge), each item gated by the kernel's
state for its own command. Impress's table borders read as text and
drag through R5.3's path; patch 0047 reports every edge's bounds and
makes the left edge drag. A line past its bound never moves against
the drag, so a still press sends nothing.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tasks/BUGS.md

@@ -151,4 +151,6 @@ P0 次序：W-01、K-01、L-01、O-01、W-02、L-02、W-03、L-03、W-04、L-04
 - [ ] P3-08 Windows（AMD）：多个 worker 同时启动时内核的 OpenCL 探测卡在驱动的 `clCreateCommandQueue` 里数分钟（`openclwrapper::switchOpenCLDevice`）；测试以 `SAL_DISABLE_OPENCL=1` 绕开；是否在 `ely.xcd` 关掉 `UseOpenCL` 待用户定
 - [ ] P3-09 Windows：内核给的选区文字与文本导出以 CRLF 换行，三个 ElyTable 单测按 LF 比对（`tests::data::sort_filter_duplicates_and_columns_run_from_their_dialogs`、`a_column_button_sorts_its_own_block_not_the_cursors`、`tests::output::exports_write_the_shown_sheet_as_text`）；导出该用哪种换行待定
 - [ ] P3-10 Windows：`crates/ely-office/tests/restart.rs` 设 `HOME` 想用临时目录，但 Windows 上 `data_dir` 取已知文件夹（不看 `HOME`），测试在真实的 ElyDoc 配置里运行；中途被杀即留下挡路的 `lok-verify.fodt` 文件夹，真实 ElyDoc 的内核核对随之失败（2026-10-14 审查中出现，已手动删去）
+- [ ] P3-11 ElyShow：正编辑表格单元格时在幻灯片空白处右键，内核（Impress）只结束编辑、不发 `LOK_CALLBACK_CONTEXT_MENU`，再右键一次才有幻灯片菜单；Windows 实测，他端未核；修需内核补丁
+- [ ] P3-12 Windows：`output::tests::targets_skip_hidden_slides_and_pad_numbers` 以 `/` 拼的路径比对，Windows 的 `join` 用 `\`，单测恒失败（代码无误）