feat(core): add console warn when editor container has no explicit he…

[ccc1110]

Summary / 摘要

Add console warning to remind developers when editor container does not have explicit height, help quickly locate blank editor rendering issue.

Motivation / 背景与动机

When users forget to set height for the editor container, the editor area will show blank without obvious error message.
This warning can output tips in browser console to reduce debugging cost.

Changes / 变更内容

• packages/core: Add container height detection logic after editor mount, print warning when computed height is 0.

• packages/core: Add corresponding unit test in editor.test.ts.

• Issue:

Note: Local Windows electron-demo test failures are caused by symlink permission limitation on Windows OS, unrelated to this core editor warning feature. CI(Linux) will run without this problem.

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