feat: add sandbox image viewing tool - #179

Closes #178

Summary

• add sandbox_view_image to read bounded image files from the active sandbox
• validate sandbox paths, image signatures, MIME types, dimensions, and file size before attaching bytes
• bridge returned google.genai.types.Part values through ADK as separate visual inputs, including multiple images
• keep binary image data out of persisted tool responses and lifecycle logs
• guide Telegram image-file uploads and restored attachments to the new tool
• register, document, and test the new capability

Validation

• uv run ruff format
• uv run ruff check
• uv run mypy .
• proxy-free full suite: 1,910 passed, 100% coverage

The four Docker contract tests could not run in this environment because Docker is not installed.