feat: runtime config, Matomo analytics, chat accounts, DM history/search, and Prometheus retention

backend/chat/src/db/db.go

@@ -45,7 +45,7 @@ func InitDB(databaseURL string) (*DBClient, string, error) {
 		return nil, driver, err
 	}
 
-	gormDB.AutoMigrate(&Message{}, &ModerationLog{}, &Media{}, &ScheduleOverride{})
+	gormDB.AutoMigrate(&Message{}, &ModerationLog{}, &Media{}, &ScheduleOverride{}, &User{})
 	log.Printf("%s database initialized (chat history, moderation log, media metadata)", strings.Title(driver))
 
 	return &DBClient{DB: gormDB}, driver, nil

backend/chat/src/db/models.go

@@ -39,6 +39,14 @@ type Media struct {
 	UpdatedAt       time.Time `gorm:"autoUpdateTime" json:"updatedAt"`
 }
 
+// User represents a registered chat user account (ADR-006).
+type User struct {
+	ID           uint      `gorm:"primarykey" json:"id"`
+	Username     string    `gorm:"uniqueIndex;size:32" json:"username"`
+	PasswordHash string    `json:"-"`
+	CreatedAt    time.Time `gorm:"autoCreateTime" json:"createdAt"`
+}
+
 // ScheduleOverride represents a scheduled playlist override (ADR-004)
 type ScheduleOverride struct {
 	ID        uint      `gorm:"primarykey" json:"id"`