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/server/tls.go

@@ -45,7 +45,7 @@ func (s *Server) loadCertificate() (tls.Certificate, error) {
 	host := s.eng.Settings().EndpointHost
 	tmpl := &x509.Certificate{
 		SerialNumber: serial,
-		Subject:      pkix.Name{CommonName: "WGX", Organization: []string{"WGX"}},
+		Subject:      pkix.Name{CommonName: "ihasvpn", Organization: []string{"ihasvpn"}},
 		NotBefore:    time.Now().Add(-time.Hour),
 		NotAfter:     time.Now().Add(3 * 365 * 24 * time.Hour),
 		KeyUsage:     x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,