docs: add OVERVIEW.md — what is Skyvern?

[Copilot]

No single document in the repo concisely answered "what does this application do?" for new contributors or evaluators.

Added OVERVIEW.md at repo root

• What it is — AI-powered browser automation using Vision LLMs + Playwright; resilient to layout changes, works on unseen sites
• How it works — Planner → Agent → Validator loop; screenshot-driven, no hardcoded selectors
• SDK surface — page.act(), page.extract(), page.validate(), page.prompt(), AI-augmented Playwright actions, higher-level page.agent.* commands
• Use cases — invoice download, form filling, data extraction, healthcare portals, e-commerce, government forms
• Deployment options — pip install, Docker Compose, Skyvern Cloud, self-hosted
• Repo map — key directories and what lives in each

Original prompt

Tell me what this application does

Created from VS Code.