refactor: modularize chat backend, update docs for .m4s segments

backend/chat/src/db/models.go

@@ -0,0 +1,57 @@
+package db
+
+import (
+	"time"
+)
+
+// Message represents a chat message (persisted in SQL DB per ADR-006)
+type Message struct {
+	ID        uint      `gorm:"primarykey" json:"id"`
+	Room      string    `json:"room"`
+	Username  string    `json:"username"`
+	Text      string    `json:"text"`
+	Timestamp time.Time `json:"timestamp"`
+	Type      string    `json:"type"` // "public", "private", "system", "moderation"
+}
+
+// ModerationLog for audit trail (immutable per ADR-005)
+type ModerationLog struct {
+	ID        uint      `gorm:"primarykey" json:"id"`
+	Action    string    `json:"action"` // "mute", "ban", "delete", "timeout"
+	Target    string    `json:"target"`
+	Moderator string    `json:"moderator"`
+	Reason    string    `json:"reason"`
+	Timestamp time.Time `json:"timestamp"`
+}
+
+// Media stores admin media library metadata (filesystem + DB model per ADR-006)
+type Media struct {
+	ID              uint      `gorm:"primarykey" json:"id"`
+	Filename        string    `gorm:"index" json:"filename"`
+	OriginalName    string    `json:"originalName"`
+	Path            string    `json:"path"`
+	SizeBytes       int64     `json:"sizeBytes"`
+	DurationSeconds int       `json:"durationSeconds"`
+	Status          string    `gorm:"index" json:"status"`
+	Title           string    `json:"title"`
+	Tags            string    `json:"tags"`
+	UploadedAt      time.Time `gorm:"autoCreateTime" json:"uploadedAt"`
+	UpdatedAt       time.Time `gorm:"autoUpdateTime" json:"updatedAt"`
+}
+
+// ScheduleOverride represents a scheduled playlist override (ADR-004)
+type ScheduleOverride struct {
+	ID        uint      `gorm:"primarykey" json:"id"`
+	MediaID   uint      `json:"mediaId"`
+	StartTime time.Time `json:"startTime"`
+	EndTime   time.Time `json:"endTime"`
+	Reason    string    `json:"reason"`
+	CreatedAt time.Time `json:"createdAt"`
+}
+
+// Presence tracks online users per room (using Redis per ADR-007)
+type Presence struct {
+	Username string `json:"username"`
+	Room     string `json:"room"`
+	Online   bool   `json:"online"`
+}