feat: Extract Card interface and CardFeedState to commons (B1)

- Create commons/ui/notifications/CardFeedState.kt with:
  - Card interface (createdAt, id)
  - CardFeedState sealed class (Loading, Loaded, Empty, FeedError)
  - DefaultCardComparator for sorting

- Update Android imports to use commons Card/CardFeedState:
  - DefaultFeedOrder.kt
  - AccountViewModel.kt
  - CardFeedContentState.kt
  - CardFeedState.kt (now only contains concrete card types)
  - CardFeedView.kt

Part of Phase B (Notifications Feed Extraction) for #1648

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/dal/DefaultFeedOrder.kt

@@ -20,8 +20,8 @@
  */
 package com.vitorpamplona.amethyst.ui.dal
 
+import com.vitorpamplona.amethyst.commons.ui.notifications.Card
 import com.vitorpamplona.amethyst.model.Note
-import com.vitorpamplona.amethyst.ui.screen.loggedIn.notifications.Card
 
 val DefaultFeedOrder: Comparator<Note> =
     compareByDescending<Note> { it.createdAt() }.thenBy { it.idHex }

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

@@ -42,6 +42,7 @@ import com.vitorpamplona.amethyst.commons.compose.GenericBaseCache
 import com.vitorpamplona.amethyst.commons.compose.GenericBaseCacheAsync
 import com.vitorpamplona.amethyst.commons.model.LiveHiddenUsers
 import com.vitorpamplona.amethyst.commons.ui.feeds.FeedState
+import com.vitorpamplona.amethyst.commons.ui.notifications.CardFeedState
 import com.vitorpamplona.amethyst.logTime
 import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.AccountSettings
@@ -82,7 +83,6 @@ import com.vitorpamplona.amethyst.ui.note.ZapraiserStatus
 import com.vitorpamplona.amethyst.ui.note.showAmount
 import com.vitorpamplona.amethyst.ui.note.showAmountInteger
 import com.vitorpamplona.amethyst.ui.screen.UiSettingsState
-import com.vitorpamplona.amethyst.ui.screen.loggedIn.notifications.CardFeedState
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.notifications.CombinedZap
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.tor.TorSettingsFlow

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/CardFeedContentState.kt

@@ -26,6 +26,8 @@ import androidx.compose.runtime.Stable
 import androidx.compose.runtime.mutableStateOf
 import com.vitorpamplona.amethyst.commons.ui.feeds.InvalidatableContent
 import com.vitorpamplona.amethyst.commons.ui.feeds.LoadedFeedState
+import com.vitorpamplona.amethyst.commons.ui.notifications.Card
+import com.vitorpamplona.amethyst.commons.ui.notifications.CardFeedState
 import com.vitorpamplona.amethyst.logTime
 import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.LocalCache

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/CardFeedState.kt

@@ -21,8 +21,7 @@
 package com.vitorpamplona.amethyst.ui.screen.loggedIn.notifications
 
 import androidx.compose.runtime.Immutable
-import androidx.compose.runtime.Stable
-import com.vitorpamplona.amethyst.commons.ui.feeds.LoadedFeedState
+import com.vitorpamplona.amethyst.commons.ui.notifications.Card
 import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.model.User
 import com.vitorpamplona.amethyst.service.firstFullCharOrEmoji
@@ -30,14 +29,6 @@ import com.vitorpamplona.quartz.nip01Core.core.ImmutableListOfLists
 import kotlinx.collections.immutable.ImmutableList
 import kotlinx.collections.immutable.toImmutableList
 import kotlinx.collections.immutable.toImmutableMap
-import kotlinx.coroutines.flow.MutableStateFlow
-
-@Immutable
-interface Card {
-    fun createdAt(): Long
-
-    fun id(): String
-}
 
 @Immutable
 class BadgeCard(
@@ -113,19 +104,3 @@ class MessageSetCard(
 
     override fun id() = note.idHex
 }
-
-@Immutable
-sealed class CardFeedState {
-    @Immutable object Loading : CardFeedState()
-
-    @Stable
-    class Loaded(
-        val feed: MutableStateFlow<LoadedFeedState<Card>>,
-    ) : CardFeedState()
-
-    @Immutable object Empty : CardFeedState()
-
-    @Immutable class FeedError(
-        val errorMessage: String,
-    ) : CardFeedState()
-}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/CardFeedView.kt

@@ -43,6 +43,8 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.commons.ui.notifications.Card
+import com.vitorpamplona.amethyst.commons.ui.notifications.CardFeedState
 import com.vitorpamplona.amethyst.logTime
 import com.vitorpamplona.amethyst.ui.actions.CrossfadeIfEnabled
 import com.vitorpamplona.amethyst.ui.feeds.FeedError

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/notifications/CardFeedState.kt

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.ui.notifications
+
+import androidx.compose.runtime.Immutable
+import androidx.compose.runtime.Stable
+import com.vitorpamplona.amethyst.commons.ui.feeds.LoadedFeedState
+import kotlinx.coroutines.flow.MutableStateFlow
+
+/**
+ * Base interface for notification cards.
+ *
+ * Cards represent grouped or individual notification items in the feed.
+ * Platform implementations provide concrete card types (NoteCard, MultiSetCard, etc.).
+ */
+@Immutable
+interface Card {
+    /**
+     * Returns the creation timestamp of this card.
+     * Used for sorting cards in chronological order.
+     */
+    fun createdAt(): Long
+
+    /**
+     * Returns a unique identifier for this card.
+     * Used for list diffing and deduplication.
+     */
+    fun id(): String
+}
+
+/**
+ * Feed state for notification cards.
+ *
+ * Mirrors FeedState but specifically typed for Card content.
+ */
+@Stable
+sealed class CardFeedState {
+    @Immutable
+    object Loading : CardFeedState()
+
+    @Stable
+    class Loaded(
+        val feed: MutableStateFlow<LoadedFeedState<Card>>,
+    ) : CardFeedState()
+
+    @Immutable
+    object Empty : CardFeedState()
+
+    @Immutable
+    class FeedError(
+        val errorMessage: String,
+    ) : CardFeedState()
+}
+
+/**
+ * Comparator for sorting cards by creation time (newest first).
+ */
+val DefaultCardComparator: Comparator<Card> =
+    compareByDescending<Card> { it.createdAt() }
+        .thenByDescending { it.id() }