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/netcfg/sysctl.go

@@ -7,7 +7,7 @@ import (
 	"strings"
 )
 
-// Sysctl is one kernel parameter and the value WGX wants for it.
+// Sysctl is one kernel parameter and the value ihasvpn wants for it.
 type Sysctl struct {
 	Key   string
 	Value string
@@ -27,7 +27,7 @@ type Result struct {
 	Err     string
 }
 
-// Wanted returns the sysctls WGX applies at startup, in order.
+// Wanted returns the sysctls ihasvpn applies at startup, in order.
 func Wanted(ipv6 bool) []Sysctl {
 	s := []Sysctl{
 		{Key: "net.ipv4.ip_forward", Value: "1", Required: true, Why: "peers cannot reach anything beyond the server without forwarding"},