fix: restore test-used functions, silence tx.Rollback closed errors, prune knip dead code

Restore processImage (images.go) and nonDepositPaymentType (handlers.go) with //nolint:unused — used in test files.
Fix 97 tx.Rollback defers to silently discard expected "tx is closed" error after commit.
Frontend: remove 44 unused shadcn-svelte files, 2 dead components, 9 stale npm deps, prune unused exports.

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

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

backend/handlers/payments/handlers.go

@@ -351,7 +351,7 @@ func CreateTerminalPayment(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()
@@ -623,7 +623,7 @@ func GetCheckoutStatus(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()
@@ -822,7 +822,7 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()
@@ -1418,6 +1418,24 @@ func buildSplitRecords(primary PaymentRecord, reqPaymentType string, info *Booki
 	return records
 }
 
+// nonDepositPaymentType picks the right label for the non-deposit portion of a
+// split payment, following the same rules as the frontend's handlePayFull:
+// 'balance' when some payment already exists, 'full' when covering everything,
+// 'partial' when leaving a remainder.
+//nolint:unused
+func nonDepositPaymentType(reqType string, totalPaidAfterThis float64, thisPortion float64, bookingTotal float64) string {
+	if totalPaidAfterThis >= bookingTotal {
+		if totalPaidAfterThis-thisPortion > 0 {
+			return "balance"
+		}
+		return "full"
+	}
+	if reqType == "full" || reqType == "deposit" {
+		return "partial"
+	}
+	return "partial"
+}
+
 func GetUserPaymentMethods(w http.ResponseWriter, r *http.Request) {
 	userID, ok := r.Context().Value(mw.UserIDKey).(string)
 	if !ok || userID == "" {
@@ -1601,7 +1619,7 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()
@@ -1947,7 +1965,7 @@ func AcquirePaymentLock(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()
@@ -1998,7 +2016,7 @@ func ReleasePaymentLock(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	defer func() {
-    if err := tx.Rollback(r.Context()); err != nil {
+    if err := tx.Rollback(r.Context()); err != nil && err.Error() != "tx is closed" {
         slog.Error("failed to rollback transaction", "err", err)
     }
 }()