Support for save/restore of the vector storage

[pqnet]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for backup and restoration of the vector storage by introducing new API endpoints.

• New POST endpoint to restore backup files with optional clearing of current documents.
• New GET endpoint to download the backup as a JSON file.
• README update with instructions on how to use the new backup and restore features.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
server/api/backup/index.post.ts	Adds a POST endpoint to restore backup data with transaction support.
server/api/backup/index.get.ts	Adds a GET endpoint to export database documents as a backup.
README.md	Updates documentation with backup and restore usage instructions.

Comments suppressed due to low confidence (1)

server/api/backup/index.post.ts:53

• [nitpick] The variable name 'prepst' is ambiguous. Consider renaming it to something more descriptive like 'insertDocStmt' to improve clarity.

const prepst = db.prepare(`insert into documents (content, metadata, embedding) values (?, jsonb(?), ?)`);