Discovery: set GitHub topics, website field, and social preview image (repo settings)

[hexsecs]

Problem

GitHub-native discovery is the biggest reach channel for a tool like this, and the repo metadata underuses it:

• No topics set — topics are GitHub's primary discovery mechanism (topic:can-bus etc.) and feed Explore/recommendations.
• The repo description starts with the docs URL pasted into the text, while the dedicated website field is empty.
• No social preview image, so the GitHub repo link itself unfurls without a card.

Suggested fix (all in the GitHub UI — Settings / About, ~5 minutes)

• Add topics: can-bus, j1939, automotive-security, car-hacking, socketcan, uds, doip, iso-tp, reverse-engineering, fuzzing, mcp, security-tools, python, cli
• Move https://hexsecs.github.io/canarchy/ into the website field and clean up the description, e.g.: "Stream-first CAN & J1939 toolkit for security research and AI agents — typed JSONL events, TUI, fuzzing, MCP server."
• Upload a social preview image (1280×640) under Settings → Social preview — reuse the CAN/ARCHY brand mark from the homepage

Acceptance criteria

Repo appears under its topics on GitHub; sharing the repo URL produces an image card; the About sidebar shows a clean description with a separate website link.