fix(onramp): re-throw CancellationException in buildSwapTransaction

When users navigate away from the Swap screen during Phantom transaction
building, viewModelScope cancellation was caught by the generic
catch(Exception) block and wrapped as FailedToCreateTransaction, causing
~3,730 spurious Bugsnag events. Re-throw CancellationException to let
coroutine cancellation propagate naturally.

Author: bmc08gt

apps/flipcash/shared/onramp/deeplinks/src/main/kotlin/com/flipcash/app/onramp/PhantomWalletController.kt

@@ -37,6 +37,7 @@ import dev.bmcreations.phantom.connect.ConnectResult
 import dev.bmcreations.phantom.connect.PhantomSdk
 import dev.bmcreations.phantom.connect.wallet.PhantomWalletConnector
 import dev.bmcreations.phantom.connect.wallet.PhantomWalletException
+import kotlin.coroutines.cancellation.CancellationException
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.NonCancellable
 import kotlinx.coroutines.withContext
@@ -225,6 +226,8 @@ class PhantomWalletController @Inject constructor(
                     }
 
                 Result.success(transaction to swapId)
+            } catch (e: CancellationException) {
+                throw e
             } catch (e: Exception) {
                 trace("External swap failed", type = TraceType.Error, error = e)
                 Result.failure(