fix(knowledgebase): restore preview/save behavior for local file uploads

[ponyfly6]

Motivation

• Users reported that uploading local text files could leave the preview/save flow unresponsive because the UI allowed advancing before upload metadata was ready and some deployments returned only filePath (no fileUrl).

Description

• Require uploaded files to be finished and to have produced document metadata before enabling the step advancement by updating nextStepAvailable in step.component.ts to check file.status() === 'done' and that file.document() exists.
• Allow estimation/preview to run when either fileUrl or filePath is present by changing the loader condition in preview.component.ts to request.fileUrl || request.filePath.
• Normalize upload response handling in KnowledgeFileUploader (knowledgebase.service.ts) by filling fileUrl from event.body.fileUrl ?? event.body.url and setting uploadedUrl accordingly to cover different backend response shapes.

Testing

• Ran lint with yarn nx run cloud:lint; the run failed due to an existing repository-level lint/runtime configuration issue (ENOENT: no such file or directory, open '/workspace/xpert/apps/cloud/src/*') that is unrelated to these changes. No unit/integration tests were added for this UI/data-flow change in this PR.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle failed uploads before gating next step

This new gate requires every local file to reach done, which turns upload errors into a hard blocker: KnowledgeFileUploader sets status = 'error' on failure, and the local-file UI only shows a delete action once progress() >= 100 (otherwise it renders a non-removal progress button), so a failed upload can become non-removable while nextStepAvailable stays false forever. In that case users cannot proceed with successfully uploaded files and must restart the flow.

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