fix(chat): enforce tip minimum on send with an alert

Guard the send path: when the chat is a tip DM with a minimum and the
entered amount is below it, surface a "<min> Minimum" alert and abort
the send instead of proceeding. Reword the tip-minimum error strings to
match.

Pairs with the slide label simplification — the minimum is now enforced
at send time rather than implied by a dedicated "Swipe to Tip" label.

Author: bmc08gt

apps/flipcash/core/src/main/res/values/strings.xml

@@ -899,8 +899,8 @@
     <string name="action_swipeToTip">Swipe to Tip</string>
     <string name="content_description_customTipAmount">Enter a custom amount</string>
     <string name="subtitle_tipHintMinimum">Minimum tip %1$s</string>
-    <string name="error_title_tipMinimum">Tips Start at %1$s</string>
-    <string name="error_description_tipMinimum">Enter a larger amount to send this tip</string>
+    <string name="error_title_tipMinimum">%1$s Minimum</string>
+    <string name="error_description_tipMinimum">Increase the amount to send</string>
     <string name="label_viaTipCard">via Tip Card</string>
 
     <string name="title_block">Block</string>

apps/flipcash/features/messenger/src/main/kotlin/com/flipcash/app/messenger/internal/ChatViewModel.kt

@@ -665,6 +665,17 @@ internal class ChatViewModel @Inject constructor(
                     val source = owner.withTimelockForToken(token)
 
                     val balance = tokenCoordinator.balanceForToken(token)
+
+                    val minimum = minAmountFlow.value
+                    if (minimum != null && amount.valueLessThan(minimum)) {
+                        dispatchEvent(Event.SendStateUpdated())
+                        BottomBarManager.showAlert(
+                            title = resources.getString(R.string.error_title_tipMinimum, minimum.formatted()),
+                            message = resources.getString(R.string.error_description_tipMinimum),
+                        )
+                        return@launch
+                    }
+
                     val verifiedFiat = verifiedFiatCalculator.compute(
                         amount = amount,
                         token = token,