chore: point repo URLs and MCP name at the hiddenstateresearch org

[willyfh]

Do not merge until the repo has been transferred to hiddenstateresearch. Before that, the new URLs 404 (no redirect exists yet in that direction).

Summary

Prepares the repo for the move from willyfh/visualtorch to hiddenstateresearch/visualtorch.

• Rewrites every github.com / raw.githubusercontent.com reference (README badges and images, setup.py, docs conf, CITATION.cff, contributing docs, install snippet, star-history script, MCP API reference base URLs).
• Renames the MCP Registry server from io.github.willyfh/visualtorch to io.github.hiddenstateresearch/visualtorch in server.json, the README mcp-name marker, the docs, and the ownership check in publish-mcp.yml. mcp-publisher login github-oidc only grants the repo owner's namespace, so the old name can't be published from an org-owned repo.
• Unchanged on purpose: @willyfh in CODEOWNERS and the GOVERNANCE maintainer list, since those name a person, not the repo.

Release ordering

The registry checks the mcp-name marker in the PyPI description, so the first release after merging must publish to PyPI with this README before the MCP publish can succeed (the existing wait step in publish-mcp.yml handles that). The old io.github.willyfh/visualtorch registry entry will stay at its last version.

Test plan

• pytest tests - 312 passed
• pre-commit run on changed files - all hooks pass
• No remaining willyfh/visualtorch references in tracked files
• After transfer: README images/badges render, docs build, star-history workflow pushes to assets