Add PgStudio to GUI section

[ric-v]

Description

Adding PgStudio to the GUI section — an open-source VS Code extension for
PostgreSQL management.

• GitHub: https://github.com/dev-asterix/PgStudio
• Marketplace: https://marketplace.visualstudio.com/items?itemName=ric-v.postgres-explorer
• License: MIT
• Actively maintained (v1.0.0, April 2026)

Checklist

• Entry is added in alphabetical order
• Format matches existing entries (name, URL, one-sentence description)
• Link goes to the GitHub repo (not a commercial page)
• Project is open source with a valid license
• Description is concise and factual