Add NetworkConfig.AllowedDomains and DeniedDomains fields for controlling
outbound connections by hostname. Deny rules are checked first (deny wins).
When AllowedDomains is set, only matching domains are permitted. When only
DeniedDomains is set, all domains except denied ones are allowed.
Implement FilteringProxy that wraps gost HTTP proxy with domain enforcement
via AllowConnect callback. Skip GreyHaven proxy/DNS defaults
Rebrand the project from Fence to Greywall, the sandboxing layer of the
GreyHaven platform. This updates:
- Go module path to gitea.app.monadical.io/monadical/greywall
- Binary name, CLI help text, and all usage examples
- Config paths (~/.config/greywall/greywall.json), env vars (GREYWALL_*)
- Log prefixes ([greywall:*]), temp file prefixes (greywall-*)
- All documentation, scripts, CI workflows, and example files
- README rewritten with GreyHaven branding and Fence attribution
Directory/file renames: cmd/fence → cmd/greywall, pkg/fence → pkg/greywall,
docs/why-fence.md → docs/why-greywall.md, example JSON files, and banner.
