fix(apps/amm): disable the already-selected token in the swap token picker

The token selector let you pick the same token on both sides of a swap.
That drove resolvePool into amm_client_pool_pda with def_a == def_b, which
hits `panic!("Definitions match")` in amm_core (a pool needs two distinct
tokens). Because that panic crosses the `#[no_mangle]` FFI boundary — which
can't unwind — it aborts, taking the whole UI process down.

Guard it at the source: the picker now disables (dims, no hover/click, tags
"Selected") whichever token is already chosen on the opposite side, so the
two sides can never match.

- TokenListItem: add a `disabled` state (opacity, inert MouseArea, tag)
- TokenSelectorModal: add `disabledDefinitionId`; gate both the popular-token
  pills and the list rows on it
- SwapPage: on open, set it to the opposite side's selected token

apps/amm/qml/components/swap/TokenListItem.qml

@@ -9,15 +9,20 @@ Item {
     property string tokenName: ""
     property string tokenSymbol: ""
     property string tokenDefinitionId: ""
+    // When true, the token is already selected on the other side of the swap,
+    // so it's shown dimmed and can't be picked (a pool needs two distinct
+    // tokens — picking the same one both sides panics amm_core's pool PDA).
+    property bool disabled: false
 
     signal clicked()
 
     implicitHeight: 56
+    opacity: root.disabled ? 0.35 : 1.0
 
     Rectangle {
         anchors.fill: parent
         radius: 12
-        color: hoverArea.containsMouse ? theme.colors.panelBg : "transparent"
+        color: (!root.disabled && hoverArea.containsMouse) ? theme.colors.panelBg : "transparent"
         Behavior on color { ColorAnimation { duration: 120 } }
 
         RowLayout {
@@ -62,13 +67,21 @@ Item {
                     }
                 }
             }
+
+            Text {
+                visible: root.disabled
+                text: qsTr("Selected")
+                color: theme.colors.textSecondary
+                font.pixelSize: 12
+            }
         }
 
         MouseArea {
             id: hoverArea
             anchors.fill: parent
-            hoverEnabled: true
-            cursorShape: Qt.PointingHandCursor
+            enabled: !root.disabled
+            hoverEnabled: !root.disabled
+            cursorShape: root.disabled ? Qt.ArrowCursor : Qt.PointingHandCursor
             onClicked: root.clicked()
         }
     }

apps/amm/qml/components/swap/TokenSelectorModal.qml

@@ -12,6 +12,10 @@ Item {
     property var theme
     property var tokens: []
     property string searchText: ""
+    // definitionId of the token already chosen on the other side of the swap.
+    // That token is shown disabled here so the two sides can never match (a
+    // same-token pool has no PDA — it panics amm_core).
+    property string disabledDefinitionId: ""
 
     signal tokenSelected(var token)
 
@@ -118,12 +122,17 @@ Item {
                 Repeater {
                     model: root.tokens.slice(0, 5)
                     delegate: Rectangle {
+                        id: pill
+                        readonly property bool isDisabled:
+                            root.disabledDefinitionId !== "" &&
+                            modelData.definitionId === root.disabledDefinitionId
                         height: 40
                         radius: 20
-                        color: pillHover.containsMouse ? theme.colors.panelHoverBg : theme.colors.panelBg
+                        color: (!pill.isDisabled && pillHover.containsMouse) ? theme.colors.panelHoverBg : theme.colors.panelBg
                         border.color: theme.colors.border
                         border.width: 1
                         width: pillRow.implicitWidth + 24
+                        opacity: pill.isDisabled ? 0.35 : 1.0
                         Behavior on color { ColorAnimation { duration: 120 } }
                         RowLayout {
                             id: pillRow
@@ -139,8 +148,9 @@ Item {
                         MouseArea {
                             id: pillHover
                             anchors.fill: parent
-                            hoverEnabled: true
-                            cursorShape: Qt.PointingHandCursor
+                            enabled: !pill.isDisabled
+                            hoverEnabled: !pill.isDisabled
+                            cursorShape: pill.isDisabled ? Qt.ArrowCursor : Qt.PointingHandCursor
                             onClicked: root.tokenSelected(modelData)
                         }
                     }
@@ -170,6 +180,8 @@ Item {
                     tokenName: modelData.name
                     tokenSymbol: modelData.symbol
                     tokenDefinitionId: modelData.definitionId
+                    disabled: root.disabledDefinitionId !== "" &&
+                              modelData.definitionId === root.disabledDefinitionId
                     onClicked: root.tokenSelected(modelData)
                 }
             }

apps/amm/qml/pages/SwapPage.qml

@@ -144,6 +144,10 @@ Item {
 
                 onRequestTokenSelect: function(side) {
                     tokenModal.targetSide = side
+                    // Disable the token already picked on the opposite side so the
+                    // two sides can't match (a same-token pool panics amm_core).
+                    var other = side === "sell" ? swapCard.buyToken : swapCard.sellToken
+                    tokenModal.disabledDefinitionId = other ? other.definitionId : ""
                     tokenModal.open()
                 }