fix(tui): fix Tab key completion in the editor

[liruifengv]

Related Issue

No related issue.

Problem

Two related Tab-key issues in the editor's autocomplete:

1. Pressing plain Tab while no completion menu is showing opens the file completion list, even though Tab is not a file-mention trigger (@ is). Tab should only accept the selected item when a menu is already open.
2. After Tab-completing a slash command name (e.g. /go -> /goal), the menu closes and never reopens, so the command's subcommands (e.g. status, pause) are not shown. For commands without subcommands, the completion also fell back to listing files.

What changed

• Swallow plain Tab in the editor when the autocomplete menu is closed, so it no longer triggers file completion. Tab still accepts the highlighted item while a menu is open.
• After a slash command name is accepted via Tab, reopen the completion menu so its subcommands appear. The reopen uses non-forced completion so commands without subcommands stay closed instead of falling back to the file list.
• Added tests covering: Tab is a no-op when the menu is closed, subcommands reopen after slash Tab-accept, and no file-list fallback for commands without subcommands.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: 27e5ec9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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[pkg-pr-new]

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commit: 27e5ec9