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

database/sqlite/sqlite.go

@@ -0,0 +1,95 @@
+package sqlite
+
+import (
+	"database/sql"
+	"fmt"
+
+	"github.com/librespeed/speedtest-go/database/schema"
+
+	_ "modernc.org/sqlite"
+	log "github.com/sirupsen/logrus"
+)
+
+type SQLite struct {
+	db *sql.DB
+}
+
+func Open(databaseFile string) *SQLite {
+	conn, err := sql.Open("sqlite", databaseFile)
+	if err != nil {
+		log.Fatalf("Cannot open SQLite database: %s", err)
+	}
+
+	// Enable WAL mode for better concurrent performance
+	if _, err := conn.Exec("PRAGMA journal_mode=WAL"); err != nil {
+		log.Warnf("Failed to set SQLite journal mode to WAL: %s", err)
+	}
+
+	// Create table if not exists (matching the PHP SQLite auto-creation behavior)
+	stmt := `CREATE TABLE IF NOT EXISTS speedtest_users (
+		id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+		timestamp DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+		ip TEXT NOT NULL,
+		ispinfo TEXT,
+		extra TEXT,
+		ua TEXT NOT NULL,
+		lang TEXT NOT NULL,
+		dl TEXT,
+		ul TEXT,
+		ping TEXT,
+		jitter TEXT,
+		log TEXT,
+		uuid TEXT
+	);`
+	if _, err := conn.Exec(stmt); err != nil {
+		log.Fatalf("Failed to create speedtest_users table: %s", err)
+	}
+
+	return &SQLite{db: conn}
+}
+
+func (p *SQLite) Insert(data *schema.TelemetryData) error {
+	var existingID int
+	// Check for duplicate UUID first
+	err := p.db.QueryRow(`SELECT id FROM speedtest_users WHERE uuid = ?`, data.UUID).Scan(&existingID)
+	if err == nil {
+		// Record with this UUID already exists - skip insert
+		return nil
+	}
+
+	stmt := `INSERT INTO speedtest_users (ip, ispinfo, extra, ua, lang, dl, ul, ping, jitter, log, uuid) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?);`
+	_, err = p.db.Exec(stmt, data.IPAddress, data.ISPInfo, data.Extra, data.UserAgent, data.Language, data.Download, data.Upload, data.Ping, data.Jitter, data.Log, data.UUID)
+	return err
+}
+
+func (p *SQLite) FetchByUUID(uuid string) (*schema.TelemetryData, error) {
+	var record schema.TelemetryData
+	row := p.db.QueryRow(`SELECT * FROM speedtest_users WHERE uuid = ?`, uuid)
+	if row != nil {
+		var id int
+		if err := row.Scan(&id, &record.Timestamp, &record.IPAddress, &record.ISPInfo, &record.Extra, &record.UserAgent, &record.Language, &record.Download, &record.Upload, &record.Ping, &record.Jitter, &record.Log, &record.UUID); err != nil {
+			return nil, fmt.Errorf("sqlite fetch by uuid: %w", err)
+		}
+	}
+	return &record, nil
+}
+
+func (p *SQLite) FetchLast100() ([]schema.TelemetryData, error) {
+	var records []schema.TelemetryData
+	rows, err := p.db.Query(`SELECT * FROM speedtest_users ORDER BY timestamp DESC LIMIT 100;`)
+	if err != nil {
+		return nil, fmt.Errorf("sqlite fetch last 100: %w", err)
+	}
+	if rows != nil {
+		defer rows.Close()
+		for rows.Next() {
+			var record schema.TelemetryData
+			var id int
+			if err := rows.Scan(&id, &record.Timestamp, &record.IPAddress, &record.ISPInfo, &record.Extra, &record.UserAgent, &record.Language, &record.Download, &record.Upload, &record.Ping, &record.Jitter, &record.Log, &record.UUID); err != nil {
+				return nil, fmt.Errorf("sqlite scan row: %w", err)
+			}
+			records = append(records, record)
+		}
+	}
+	return records, nil
+}