feat(computer-use): add Linux backend

[tyy130]

Summary

• add a first-class Linux computer_use backend that launches the linux-computer-use MCP driver
• auto-select Linux vs macOS backend behind the existing model-facing computer_use schema
• update install/status/tool setup docs for platform drivers
• add Linux backend adapter tests and keep existing macOS/noop coverage

Verification

• python -m pytest tests/hermes_cli/test_tools_config.py tests/hermes_cli/test_post_setup_gating.py tests/hermes_cli/test_tools_disable_enable.py tests/hermes_cli/test_commands.py tests/cli/test_cli_tools_command.py tests/tools/test_computer_use.py tests/tools/test_computer_use_linux_backend.py tests/tools/test_computer_use_capture_routing.py tests/test_packaging_metadata.py -q -o 'addopts=' → 391 passed
• python -m hermes_cli.main computer-use status → detected linux-computer-use on local Cinnamon/X11
• HERMES_COMPUTER_USE_BACKEND=linux handle_computer_use capture smoke → returned Linux terminal capture JSON

[teknium1]

Superseded by #50552, which added a first-class cross-platform cua-driver runtime — Linux (alongside macOS and Windows), auto-selected behind the existing model-facing computer_use schema, with install/status/doctor wired through hermes computer-use. That covers the Linux support this PR set out to add, using the same cua-driver-rs backend the rest of the toolset now uses (rather than a separate Linux MCP driver). Thanks for the contribution and for pushing on Linux support — closing as superseded by the merged cross-platform work.