Rename the project to ihasvpn

WGX shares its name with several other WireGuard tools, so the project
becomes ihasvpn, alongside ihasmail.

- Module github.com/Coffey-Labs/ihasvpn, command cmd/ihasvpn, image
  ghcr.io/coffey-labs/ihasvpn.
- Environment variables move from WGX_* to IHASVPN_*. The default database
  is ihasvpn.db, the nftables table is `ihasvpn`, metrics are ihasvpn_*, and
  the session cookie and theme key are renamed, so existing sessions end.
- The mark is the ihasmail cat peeking over the edge of a shield, drawn as
  a vector. docs/brand/generate.py builds the mark, mono mark, wordmarks,
  social card, favicons and app icons from that one drawing.
- The console takes ihasmail's palette: the ihasmail.org teal-navy for dark,
  its contrast-checked light tiers with the site's light accent, received
  traffic in the cat's orange and sent in teal. The wordmark weight and
  font stack follow ihasmail.org.
- Detail values wrap at spaces before breaking inside an address, so an
  IPv6 tunnel address no longer splits mid-number.
- The README history note about the earlier WGX installer is gone with the
  name it explained. Screenshots retaken.

internal/wg/linux.go

@@ -23,7 +23,7 @@ import (
 // linuxBackend drives a real WireGuard interface. In kernel mode the link is a
 // native `wireguard` netlink link and every packet is handled by the module;
 // in userspace mode a wireguard-go process owns a TUN device with the same
-// name and WGX talks to it over its UAPI socket. Both are configured through
+// name and ihasvpn talks to it over its UAPI socket. Both are configured through
 // wgctrl, which picks the transport on its own.
 type linuxBackend struct {
 	name      string
@@ -38,7 +38,7 @@ type linuxBackend struct {
 // trusting /sys/module, because a module that is loadable but not yet loaded
 // is only discovered by asking for it.
 func KernelAvailable() bool {
-	const probe = "wgxprobe0"
+	const probe = "ihasvpnprobe0"
 	link := &netlink.Wireguard{LinkAttrs: netlink.LinkAttrs{Name: probe}}
 	if err := netlink.LinkAdd(link); err != nil {
 		return false