增加了基础的块功能

docs/editor-checklist.md

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+# Editor Quick Checklist
+
+1. Select 2-3 paragraphs, open block menu, convert to code block.
+Expected: merged into 1 code block, selection remains on that block.
+
+2. Select 2-3 contiguous blocks, click move up/down.
+Expected: all selected blocks move together in one step.
+
+3. Select 2-3 contiguous blocks, drag using the block handle.
+Expected: drag preview shows "will move N blocks", all blocks move together.
+
+4. Select multiple blocks, run copy/delete/duplicate from block menu.
+Expected: operation applies to all selected blocks.
+
+5. After each multi-block action, press `Ctrl/Cmd + Z` once.
+Expected: the full action is reverted in one undo step.
+
+6. Open block menu and expand "查看快捷键".
+Expected: shortcuts are visible and menu remains usable.