feat(user): extend DeleteAccountHandler with external system scrubbing

DeleteAccountHandler now scrubs external systems BEFORE SQL-level anonymization. S3: deletes profile picture from S3/R2 (profiles/{userID}.jpg) when s3.Client is configured. Square: iterates user's saved cards and calls DeleteCardOnFile for each non-deleted card when payments.SquareClient is configured. Both run in background goroutines (non-blocking, best-effort with warning logs). CardDAV contact deletion remains as existing best-effort goroutine.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/handlers/user/account.go

@@ -1,13 +1,17 @@
 package user
 
 import (
+	"context"
 	"database/sql"
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 
 	"crussell/db"
+	"crussell/handlers/payments"
 	"crussell/internal/dav"
+	"crussell/internal/s3"
 	"crussell/mw"
 )
 
@@ -20,26 +24,71 @@ func DeleteAccountHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var accountRole string
-	err := db.DB.QueryRow(r.Context(), `SELECT account_role FROM users WHERE id = $1`, userID).Scan(&accountRole)
+	var profilePicURL sql.NullString
+	err := db.DB.QueryRow(r.Context(), `SELECT account_role, profile_pic_url FROM users WHERE id = $1`, userID).
+		Scan(&accountRole, &profilePicURL)
 	if err != nil {
 		if err == sql.ErrNoRows {
 			http.Error(w, "user not found", http.StatusNotFound)
 			return
 		}
-		log.Printf("Failed to fetch user role for deletion: %v", err)
+		log.Printf("Failed to fetch user for deletion: %v", err)
 		http.Error(w, "server error", http.StatusInternalServerError)
 		return
 	}
 
+	ctx := r.Context()
+
+	// --- External system scrubbing (BEFORE SQL anonymize) ---
+
+	// Delete profile picture from S3/R2
+	if profilePicURL.Valid && profilePicURL.String != "" && s3.Client != nil {
+		go func(picURL string) {
+			bucket := os.Getenv("S3_PROFILE_PICS_BUCKET")
+			if bucket == "" {
+				bucket = "crussell-profile-pics"
+			}
+			// profiles/{userID}.jpg — matches UploadProfilePictureHandler key format
+			key := fmt.Sprintf("profiles/%s.jpg", userID)
+			if err := s3.Client.Delete(context.Background(), bucket, key); err != nil {
+				log.Printf("Warning: Failed to delete profile picture for user %s: %v", userID, err)
+			}
+		}(profilePicURL.String)
+	}
+
+	if payments.SquareClient != nil {
+		go func() {
+			rows, err := db.DB.Query(ctx,
+				`SELECT square_card_id FROM user_saved_cards WHERE user_id = $1 AND deleted_at IS NULL`, userID)
+			if err != nil {
+				log.Printf("Warning: Failed to query saved cards for user %s: %v", userID, err)
+				return
+			}
+			defer rows.Close()
+			for rows.Next() {
+				var cardID string
+				if err := rows.Scan(&cardID); err != nil {
+					log.Printf("Warning: Failed to scan card ID for user %s: %v", userID, err)
+					continue
+				}
+				if err := payments.SquareClient.DeleteCardOnFile(context.Background(), cardID); err != nil {
+					log.Printf("Warning: Failed to delete Square card %s for user %s: %v", cardID, userID, err)
+				}
+			}
+		}()
+	}
+
+	// --- SQL-level anonymization/deletion ---
+
 	if accountRole == "guest" {
-		_, err = db.DB.Exec(r.Context(), `SELECT delete_guest_user($1)`, userID)
+		_, err = db.DB.Exec(ctx, `SELECT delete_guest_user($1)`, userID)
 		if err != nil {
 			log.Printf("Failed to delete guest user %s: %v", userID, err)
 			http.Error(w, "server error", http.StatusInternalServerError)
 			return
 		}
 	} else {
-		_, err = db.DB.Exec(r.Context(), `SELECT anonymize_user($1)`, userID)
+		_, err = db.DB.Exec(ctx, `SELECT anonymize_user($1)`, userID)
 		if err != nil {
 			log.Printf("Failed to anonymize user %s: %v", userID, err)
 			http.Error(w, "server error", http.StatusInternalServerError)