fix(web): search files in initial workspace drafts

[xianjianlf2]

Related Issue

Resolve #2189

Problem

See linked issue. In the empty workspace draft state, file mention search had no active session and returned no matches before the first message created a session.

What changed

• Added a workspace-scoped file search route that reuses the same filename search behavior as session filesystem search.
• Updated kimi-web file mention search to use session search when a session exists and workspace search while drafting the first prompt.
• Added route coverage for searching workspace files before session creation and for unknown workspace errors.

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: d31a181

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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