feat(resolver): broad host evidence discovery, virtual package (Provides) resolution & --no-deps flag

[brasga-a]

Summary

This PR establishes broad host evidence discovery and virtual package resolution to solve cross-distribution dependency resolution failures (such as installing foreign .deb packages on Arch Linux or .rpm packages on Debian/Ubuntu), and adds the --no-deps flag for standalone installations.

Key Changes

1. Broad Host Evidence Discovery (crates/pkg-core/src/resolver/evidence.rs):
   • Dynamic executable discovery: Scans /bin and /usr/bin (~1.3ms runtime) replacing hardcoded lists with dynamic system executable capabilities (bin:<cmd>).
   • Desktop & System Subsystem Probes: Probes D-Bus (feature:default-dbus-session-bus, feature:dbus-session-bus), GSettings/DConf (feature:gsettings-backend, feature:dconf-gsettings-backend), Wayland, X11, PipeWire, PulseAudio, ALSA, CA certificates, and desktop integration resources.
   • Passive Native Host Package Inspection: Inspects Arch Linux (/var/lib/pacman/local/*/desc) and Debian/Ubuntu (/var/lib/dpkg/status) without root for installed packages and their declared %PROVIDES% / Provides: fields.
2. Virtual Package Resolution (crates/pkg-core/src/resolver/mod.rs):
   • Package constraints (Constraint::Package) can now be satisfied by virtual package providers (both in repositories via pkg.provides / pkg.versioned_provides and from host evidence) while strictly upholding INV-007 cross-distro nominal safety boundaries.
3. CLI & MCP --no-deps / --skip-deps Flag (crates/pkg-cli, pkg-core):
   • Adds --no-deps (alias --skip-deps) to pkg install and the MCP pkg.install tool, allowing users to install standalone packages without cascading dependency resolution.

Verification

• 88 unit tests in pkg-core passed.
• 26 integration test suites in pkg-cli passed, including new tests:
  • test_virtual_package_resolved_via_repository_provides
  • test_virtual_package_satisfied_via_host_feature_evidence
  • test_install_options_skip_dependencies
  • test_cli_install_with_no_deps_flag
  • test_cli_install_with_skip_deps_alias
• cargo test --workspace passed with 0 failures.