Replace 'uv add .' with 'uv sync' in local-server.mdx to ensure it can be workable without self-dependencie error

[wyzBelinda]

when you new langgraph agent demo, you need to get all of its dependencies. while you use "uv add ." will cause self-dependencies and get an error as below. merging this request will help people who really "getting started" avoid facing more mistakes and get stucked.

TO fix ：
error: Requirement name agent matches project name agent, but self-dependencies are not permitted without the --dev or --optional flags. If your project name (agent) is shadowing that of a third-party dependency, consider renaming the project.

Overview

Type of change

Type: [Replace with: New documentation page / Update existing documentation / Fix typo/bug/link/formatting / Remove outdated content / Other]

Related issues/PRs

• GitHub issue:
• Feature PR:

• Linear issue:
• Slack thread:

Checklist

• I have read the contributing guidelines
• I have tested my changes locally using docs dev
• All code examples have been tested and work correctly
• I have used root relative paths for internal links
• I have updated navigation in src/docs.json if needed

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Additional notes