Sync PHP backend feature parity: IP detection, database backends, API endpoints, and frontend

- IP detection: Cloudflare IPv6, ULA IPv6, proxy header chain, offline GeoIP DB
- Database: add SQLite (pure Go, no CGo) and MSSQL backends
- API: add JSON result sharing endpoint and ID obfuscation
- Frontend: add modern CSS design, design switcher, favicon
- Compatibility: ?cors parameter support, human-friendly distance rounding
- Update Go to 1.21, add modernc.org/sqlite and maxminddb deps

go.mod

@@ -1,10 +1,11 @@
 module github.com/librespeed/speedtest-go
 
-go 1.16
+go 1.25.0
 
 require (
 	github.com/breml/rootcerts v0.2.1
 	github.com/coreos/go-systemd/v22 v22.4.0
+	github.com/denisenkom/go-mssqldb v0.12.3
 	github.com/go-chi/chi/v5 v5.0.7
 	github.com/go-chi/cors v1.2.0
 	github.com/go-chi/render v1.0.1
@@ -14,12 +15,42 @@ require (
 	github.com/gorilla/sessions v1.2.1
 	github.com/lib/pq v1.10.4
 	github.com/oklog/ulid/v2 v2.0.2
+	github.com/oschwald/maxminddb-golang v1.13.1
 	github.com/pires/go-proxyproto v0.6.1
 	github.com/sirupsen/logrus v1.8.1
-	github.com/spf13/afero v1.8.0 // indirect
 	github.com/spf13/viper v1.10.1
 	github.com/umahmood/haversine v0.0.0-20151105152445-808ab04add26
 	go.etcd.io/bbolt v1.3.6
 	golang.org/x/image v0.0.0-20211028202545-6944b10bf410
-	golang.org/x/sys v0.0.0-20220114195835-da31bd327af9 // indirect
+	modernc.org/sqlite v1.50.0
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/fsnotify/fsnotify v1.5.1 // indirect
+	github.com/golang-sql/civil v0.0.0-20190719163853-cb61b32ac6fe // indirect
+	github.com/golang-sql/sqlexp v0.1.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/hashicorp/hcl v1.0.0 // indirect
+	github.com/kr/pretty v0.2.0 // indirect
+	github.com/magiconair/properties v1.8.5 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/mitchellh/mapstructure v1.4.3 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/pelletier/go-toml v1.9.4 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	github.com/spf13/afero v1.8.0 // indirect
+	github.com/spf13/cast v1.4.1 // indirect
+	github.com/spf13/jwalterweatherman v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/subosito/gotenv v1.2.0 // indirect
+	golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d // indirect
+	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/text v0.3.7 // indirect
+	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
+	gopkg.in/ini.v1 v1.66.2 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	modernc.org/libc v1.72.0 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
 )