Contract model-visible terminal tools

[liusihang]

Summary

• Contract model-visible OpenAPI tools to core terminal/file/process primitives while hiding convenience endpoints from schema.
• Add get_environment, guarded write_file overwrite semantics, and apply_patch with dry-run/conflict reporting.
• Document response schemas/examples and include ripgrep in the full runtime image.

Tests

• uv run --dev pytest tests/test_tool_contract.py
• uv run --dev python -m compileall open_terminal tests