Refresh current client screenshots and Starling docs

[SetZero]

Changes

• Replace desktop screenshots with current client captures using diverse sample users and reusable profile images.
• Remove published screenshot scaffolding and superseded images; use current interface labels without naming a UI design.
• Rewrite audio, connection, personalization, and staged file-sharing workflows for the current client.
• Replace retired C++ server/plugin configuration recipes with Starling service guidance.
• Add a Migrating to Starling guide covering backups, configuration conversion, database import, verification, and separately migrated data.

Verification

• Local Astro build: 62 pages generated successfully.
• All built internal page and asset references resolve.
• Visually inspected current chat, polls, previews, file attachments/options, profiles, settings, and screen sharing.
• Screenshots render actual React components with deterministic native/server fixtures; capture provenance is documented in README.