fix: correct CLI syntax - use -p flag for non-interactive mode

- Add -p flag to all one-shot command examples
- Document non-interactive mode limitations (no file writes, no shell)
- Add --yolo mode documentation
- Add --output-format json example
- Update shell alias usage examples
- Clarify Google Search works in interactive mode

docs: expand README with config sharing, MCP notes, and more examples

- Add detailed usage examples (sandbox, search grounding)
- Document ~/.gemini folder structure and GEMINI.md
- Add MCP support section with limitations and workarounds
- Clarify OAuth and Vertex AI authentication options
- Update docker-compose with host mount and Vertex AI profile
- Add shell alias convenience section
- Add built-in tools documentation