feat(docker): add isolated_paths for per-repo container-only dirs like node_modules

[radim10]

Overview

On macOS/Windows hosts the Docker sandbox shares the host's node_modules, which only has host-platform native binaries (Nx, esbuild, swc, …), so they fail in the Linux container. An npm ci/bun install inside the sandbox also overwrites the host's install.

This adds an opt-in isolated_paths setting that mounts a per-repo Docker volume over each listed directory, so the container gets its own copy and the host's is never touched:

[sandbox]
backend = "docker"
isolated_paths = ["node_modules"]

Or per run: --docker-isolated-paths node_modules,.venv.

Changes

• Per-repo volume per path, persisted across runs; a one-time hint on first use says to install inside the sandbox
• Path validation (relative, no ..) in agent validate and at run time
• agent docker cleanup --isolated-paths to list/remove the volumes
• Docs: "Isolated paths" section, plus the missing agent docker shell section from feat(docker): add agent docker shell and persist global npm/pip installs in agent home #45

Notes

• Policy fingerprints change once for all profiles (audit logs only, same as when memory/cpus were added)
• Tested end to end on macOS, including a real Nx + Bun monorepo; not tested on Linux/Windows hosts