feat: sync ephemeral transient messages

Sync telesrv 570ccf8 (feat(ephemeral): implement Layer 228 transient messages).

Skipped telesrv docs changes per public sync rules; normalized the public appearance seed label.

internal/store/postgres/ephemeral_report.go

@@ -0,0 +1,49 @@
+package postgres
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"telesrv/internal/domain"
+	"telesrv/internal/store/postgres/sqlcgen"
+)
+
+// EphemeralReportStore persists the low-volume abuse-review evidence path.
+// The hot ephemeral send/edit/delete path remains entirely in Redis.
+type EphemeralReportStore struct {
+	db sqlcgen.DBTX
+}
+
+func NewEphemeralReportStore(db sqlcgen.DBTX) *EphemeralReportStore {
+	return &EphemeralReportStore{db: db}
+}
+
+func (s *EphemeralReportStore) CreateEphemeralReport(ctx context.Context, report domain.EphemeralAbuseReport) (bool, error) {
+	if s == nil || s.db == nil {
+		return false, fmt.Errorf("ephemeral report store is not configured")
+	}
+	if err := report.Validate(); err != nil {
+		return false, err
+	}
+	evidence, err := json.Marshal(report.Evidence)
+	if err != nil {
+		return false, fmt.Errorf("marshal ephemeral report evidence: %w", err)
+	}
+	tag, err := s.db.Exec(ctx, `
+INSERT INTO ephemeral_abuse_reports (
+  reporter_user_id, channel_id, ephemeral_message_id, sender_user_id,
+  receiver_user_id, report_option, report_comment, comment_hash,
+  payload_hash, evidence, created_at
+) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10::jsonb, $11)
+ON CONFLICT (
+  reporter_user_id, channel_id, ephemeral_message_id, report_option, comment_hash
+) DO NOTHING
+`, report.ReporterUserID, report.Evidence.Peer.ID, report.Evidence.MessageID,
+		report.Evidence.SenderUserID, report.Evidence.ReceiverUserID,
+		report.Option, report.Comment, report.CommentHash[:], report.Evidence.PayloadHash[:], evidence, report.CreatedAt)
+	if err != nil {
+		return false, fmt.Errorf("insert ephemeral abuse report: %w", err)
+	}
+	return tag.RowsAffected() == 1, nil
+}