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

settings.toml

@@ -20,17 +20,25 @@ statistics_password="PASSWORD"
 # redact IP addresses
 redact_ip_addresses=false
 
-# database type for statistics data, currently supports: none, memory, bolt, mysql, postgresql
+# database type for statistics data, currently supports: none, memory, bolt, mysql, postgresql, sqlite, mssql
 # if none is specified, no telemetry/stats will be recorded, and no result PNG will be generated
 database_type="memory"
 database_hostname=""
 database_name=""
 database_username=""
 database_password=""
+# database port (optional, defaults to driver default)
+database_port=""
 
 # if you use `bolt` as database, set database_file to database file location
+# if you use `sqlite` as database, set database_file to database file location
 database_file="speedtest.db"
 
+# GeoIP offline database (.mmdb format) for ISP and country detection when ipinfo.io API is not available
+# This is used as a fallback, matching the PHP backend behavior.
+# Leave empty to disable.
+# geoip_database_file="country_asn.mmdb"
+
 # TLS and HTTP/2 settings. TLS is required for HTTP/2
 enable_tls=false
 enable_http2=false