feat(config): expose charset, loc, and parseTime as configurable DSN parameters

- add Config.Charset (MYSQL_CHARSET, default "utf8mb4"): connection character set
  sent as SET NAMES during handshake; previously hardcoded
- add Config.Loc (MYSQL_LOC, default "UTC"): IANA timezone for time.Time ↔
  DATE/DATETIME conversion; previously hardcoded
- add Config.ParseTime (MYSQL_PARSE_TIME, default "true"): driver-level DATE/DATETIME
  → time.Time mapping; valid values "true"/"false"; previously hardcoded
- update DSN() to derive parameters from Config fields with empty-means-default
  semantics; existing Config literals produce identical DSN output (backward compatible)
- remove unused url.URL construction from DSN(); params now built directly via url.Values
- document collation DSN limitation in Config godoc, CLAUDE.md, RELEASE.md, CHANGELOG.md:
  go-sql-driver v1.8.x uses 1-byte handshake collation IDs (max 255); MariaDB 11.4+
  collations such as utf8mb4_uca1400_as_cs exceed that range — set collation at the
  database/table level in schema migrations instead

mysql.go

@@ -50,6 +50,16 @@ type UnitOfWork interface {
 }
 
 // Config holds MySQL connection settings.
+//
+// DSN parameters Charset, Loc, and ParseTime default to "utf8mb4", "UTC", and
+// "true" respectively when left empty, preserving the behaviour of v0.9.0.
+// Set them explicitly when you need non-default values (e.g. Loc="Local").
+//
+// Note on Collation: go-sql-driver v1.8.x negotiates the connection collation
+// via a 1-byte handshake ID (max 255). MariaDB 11.4+ collations such as
+// utf8mb4_uca1400_as_cs carry IDs > 255 and cannot be set through the DSN
+// collation parameter. Set the desired collation at the database/table level
+// in your schema migrations instead.
 type Config struct {
 	Host            string `env:"MYSQL_HOST,required"`
 	Port            int    `env:"MYSQL_PORT"               envDefault:"3306"`
@@ -60,20 +70,38 @@ type Config struct {
 	MinConns        int    `env:"MYSQL_MIN_CONNS"          envDefault:"2"`
 	MaxConnLifetime string `env:"MYSQL_MAX_CONN_LIFETIME"  envDefault:"1h"`
 	MaxConnIdleTime string `env:"MYSQL_MAX_CONN_IDLE_TIME" envDefault:"30m"`
+	// Charset is the connection character set sent as SET NAMES <charset>.
+	// Defaults to "utf8mb4" when empty.
+	Charset string `env:"MYSQL_CHARSET" envDefault:"utf8mb4"`
+	// Loc is the IANA timezone name used for time.Time ↔ MySQL DATETIME
+	// conversion. Defaults to "UTC" when empty.
+	Loc string `env:"MYSQL_LOC" envDefault:"UTC"`
+	// ParseTime controls whether the driver maps DATE/DATETIME columns to
+	// time.Time. Valid values: "true", "false". Defaults to "true" when empty.
+	ParseTime string `env:"MYSQL_PARSE_TIME" envDefault:"true"`
 }
 
 // DSN constructs a MySQL DSN from the configuration.
+// Empty Charset, Loc, and ParseTime fields fall back to their safe defaults
+// ("utf8mb4", "UTC", "true"), matching the behaviour of v0.9.0.
 func (c Config) DSN() string {
-	u := &url.URL{
-		Scheme: "mysql",
-		User:   url.UserPassword(c.User, c.Password),
-		Host:   fmt.Sprintf("%s:%d", c.Host, c.Port),
-		Path:   "/" + c.Name,
+	charset := c.Charset
+	if charset == "" {
+		charset = "utf8mb4"
 	}
-	q := u.Query()
-	q.Set("parseTime", "true")
-	q.Set("loc", "UTC")
-	u.RawQuery = q.Encode()
+	loc := c.Loc
+	if loc == "" {
+		loc = "UTC"
+	}
+	parseTime := c.ParseTime
+	if parseTime == "" {
+		parseTime = "true"
+	}
+
+	q := url.Values{}
+	q.Set("charset", charset)
+	q.Set("loc", loc)
+	q.Set("parseTime", parseTime)
 	// go-sql-driver uses user:pass@tcp(host:port)/db?params
 	return fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?%s",
 		c.User, c.Password, c.Host, c.Port, c.Name, q.Encode())