feat: add FAB to create a public chat on the Public Chats screen

Adds a "+" FloatingActionButton to the Public Chats screen (reached from
the left drawer) that navigates to the NIP-28 channel-creation flow
(Route.ChannelMetadataEdit with no id), mirroring the create-public-chat
action already offered by the Messages FAB.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SDKFHhUqcDJvNEA7s7Qspm

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

@@ -0,0 +1,52 @@
+/*
+ * 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.ui.screen.loggedIn.publicChats
+
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.FloatingActionButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
+import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
+import com.vitorpamplona.amethyst.ui.navigation.navs.INav
+import com.vitorpamplona.amethyst.ui.navigation.routes.Route
+import com.vitorpamplona.amethyst.ui.stringRes
+import com.vitorpamplona.amethyst.ui.theme.Size26Modifier
+import com.vitorpamplona.amethyst.ui.theme.Size55Modifier
+
+@Composable
+fun NewPublicChatButton(nav: INav) {
+    FloatingActionButton(
+        onClick = { nav.nav(Route.ChannelMetadataEdit()) },
+        modifier = Size55Modifier,
+        shape = CircleShape,
+        containerColor = MaterialTheme.colorScheme.primary,
+    ) {
+        Icon(
+            symbol = MaterialSymbols.Add,
+            contentDescription = stringRes(id = R.string.new_public_chat),
+            modifier = Size26Modifier,
+            tint = Color.White,
+        )
+    }
+}

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

@@ -32,6 +32,7 @@ import com.vitorpamplona.amethyst.ui.feeds.ScrollStateKeys
 import com.vitorpamplona.amethyst.ui.feeds.WatchLifecycleAndUpdateModel
 import com.vitorpamplona.amethyst.ui.layouts.DisappearingScaffold
 import com.vitorpamplona.amethyst.ui.navigation.bottombars.AppBottomBar
+import com.vitorpamplona.amethyst.ui.navigation.bottombars.FabBottomBarPadded
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
@@ -73,6 +74,11 @@ fun PublicChatsScreen(
                 }
             }
         },
+        floatingButton = {
+            FabBottomBarPadded(nav) {
+                NewPublicChatButton(nav)
+            }
+        },
         accountViewModel = accountViewModel,
     ) {
         RefresheableBox(publicChatsFeedContentState, true) {

amethyst/src/main/res/values/strings.xml

@@ -334,6 +334,7 @@
     and thus chat messages disappear over time</string>
 
     <string name="public_chat">Public Chat</string>
+    <string name="new_public_chat">Create a new public chat</string>
     <string name="marmot_group">MLS Group</string>
     <string name="marmot_group_no_messages_yet">No messages yet</string>
     <string name="public_chat_title">Public Chat Metadata</string>