Add Pixir agent

[ranvier2d2]

Summary

Adds Pixir to the ACP Registry.

Pixir is an OTP-native, local-first coding-agent harness with ACP over stdio. It is distributed through a small npx wrapper that installs/uses the published Hex escript and launches pixir acp.

• ID: pixir
• Version: 0.1.3
• Distribution: npx @ranvier-technologies/pixir-acp@0.1.3
• Package source: https://github.com/Ranvier-Technologies/pixir-acp-npx
• Website: https://pixir.dev
• Auth: initialize advertises pixir-login with type: "terminal"
• Icon: 16x16 monochrome SVG using currentColor

Validation

Ran locally from the registry repo root:

uv run --with jsonschema python .github/workflows/build_registry.py
uv run python .github/workflows/verify_agents.py --agent pixir --type npx --auth-check --verbose

The auth check installed the published npx package and passed with:

Auth OK: pixir-login(terminal)