Fix model selection when ZCode is installed

Fixed

• Selecting a model no longer fails with “Worker profiles need unique IDs and an installed harness type” when ZCode is installed and an automatic team is enabled. Automatic teams now leave ZCode out of their model catalog because it does not support team tools yet.
• Selecting a ZCode model turns off an unused team and runs it as a single agent. Switching back to another harness keeps working.

Known limitations

• ZCode cannot lead or join agent teams yet. If a team has already run workers, start a new task to use ZCode; the existing team history is preserved.
• The model-picker fix was verified in Chromium and WebKit. Packaged installers have not been tested by hand on real hardware.

Installing

• macOS (Apple silicon): open PandaCode-macOS-arm64.dmg and drag PandaCode to Applications. This build is signed and notarized, so macOS opens it without a warning.
• macOS (Intel): the same, with PandaCode-macOS-x64.dmg.
• Windows x64: run PandaCode-Windows-x64-setup.exe. If SmartScreen warns about an unknown publisher, choose More info > Run anyway.
• Windows arm64: run PandaCode-Windows-arm64-setup.exe (same SmartScreen step).
• Linux x64: chmod +x PandaCode-Linux-x86_64.AppImage and run it.
• Linux arm64: chmod +x PandaCode-Linux-aarch64.AppImage and run it.
• Any of the above, from a terminal: npx pandacode downloads, verifies and installs the right build, and signs it locally on macOS, so no Gatekeeper warning appears.

Each file has a .sha256 checksum beside it. Installed copies update themselves from this page. Build from source: see CONTRIBUTING.md.