[FXC-6492] fix(): validate ImportedSurface DraftContext before draft submission

[benflexcompute]

Summary

• Move the ImportedSurface-requires-DraftContext guard check before Draft.create(...).submit() to prevent orphan server-side drafts when validation fails.
• Previously the validation ran after the draft was already created on the server, leaving behind orphan drafts on every failed attempt.

Test plan

• Verify that calling run() with ImportedSurface outside a DraftContext raises Flow360ValueError without creating a server-side draft
• Verify that the happy path (ImportedSurface inside DraftContext) still works correctly

🤖 Generated with Claude Code

---

Note

Low Risk
Low risk change that only reorders a precondition check in Project._run; main impact is on when an error is raised during submission, not on successful runs.

Overview
Prevents orphan server-side drafts by moving the ImportedSurface-requires-DraftContext guard to run before Draft.create(...).submit() in Project._run.

Now, calling run() with params.private_attribute_asset_cache.imported_surfaces outside an active draft context fails fast with Flow360ValueError without creating a draft.

^{Written by Cursor Bugbot for commit a312867. This will update automatically on new commits. Configure here.}