fix: let Save commit a typed-but-unadded Cashu mint

When adding a Cashu wallet, the mint URL typed into the input field was
only committed to the mint list when the user pressed the "+" button. The
Save button was gated on the list being non-empty, so a user who typed a
mint, chose a key option, and tried to Save found the button disabled with
no obvious reason — they had to discover the "+" button first.

Save now folds a pending mint from the input field into the list, making
"+" optional. The button also enables when the input is non-blank.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VX5wkwXbvoQpadALx1ZVjk

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/wallet/AddCashuWalletScreen.kt

@@ -426,16 +426,28 @@ fun AddCashuWalletScreen(
 
             Spacer(modifier = Modifier.height(24.dp))
 
+            // A mint typed into the input but not yet committed with the "+"
+            // button. Folding it into the save makes "+" optional: the user can
+            // type a mint and hit Save directly instead of being blocked by a
+            // disabled button with no obvious reason.
+            val pendingMint = mintInput.trim().trimEnd('/')
+
             Button(
                 onClick = {
+                    val allMints =
+                        if (pendingMint.isNotEmpty() && pendingMint !in mints) {
+                            mints.toList() + pendingMint
+                        } else {
+                            mints.toList()
+                        }
                     viewModel.saveWallet(
-                        mints = mints.toList(),
+                        mints = allMints,
                         keyMode = keyMode,
                         manualPrivkey = manualPrivkey.takeIf { keyMode == CashuWalletViewModel.P2pkKeyMode.Manual },
                     )
                 },
                 enabled =
-                    mints.isNotEmpty() &&
+                    (mints.isNotEmpty() || pendingMint.isNotEmpty()) &&
                         createState !is CashuWalletCreateState.Saving &&
                         (keyMode != CashuWalletViewModel.P2pkKeyMode.Manual || manualPrivkey.isNotBlank()),
                 modifier = Modifier.fillMaxWidth(),