fix(location): single location control on the geo-post screen

The geo-post composer showed two locations: the static external-id marker at the
top and the new "Posting to · Change" row below the message. Drop the duplicate
and, for the geohash case, render the interactive channel control (with retarget)
in the marker's place. Non-geohash external ids still use DisplayExternalId.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YU8YLcjH9ALr4PgdAkGPZh

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/nip22Comments/GenericCommentPostScreen.kt

@@ -106,6 +106,7 @@ import com.vitorpamplona.amethyst.ui.theme.StdVertSpacer
 import com.vitorpamplona.amethyst.ui.theme.SuggestionListDefaultHeightPage
 import com.vitorpamplona.amethyst.ui.theme.replyModifier
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip73ExternalIds.location.GeohashId
 import kotlinx.collections.immutable.persistentListOf
 import kotlinx.collections.immutable.toImmutableList
 import kotlinx.collections.immutable.toImmutableSet
@@ -244,9 +245,16 @@ private fun GenericCommentPostBody(
         ) {
             Column(Modifier.fillMaxWidth().verticalScroll(scrollState, reverseScrolling = true)) {
                 postViewModel.externalIdentity?.let {
-                    Row {
-                        DisplayExternalId(it, accountViewModel, nav)
+                    if (it is GeohashId) {
+                        // Geo-post: the interactive location channel (with retarget) replaces
+                        // the static external-id marker so there's a single location control.
+                        GeoPostLocationChannel(postViewModel)
                         Spacer(modifier = StdVertSpacer)
+                    } else {
+                        Row {
+                            DisplayExternalId(it, accountViewModel, nav)
+                            Spacer(modifier = StdVertSpacer)
+                        }
                     }
                 }
 
@@ -311,8 +319,6 @@ private fun GenericCommentPostBody(
                     )
                 }
 
-                GeoPostLocationChannel(postViewModel)
-
                 DisplayPreviews(postViewModel.urlPreviews, accountViewModel, nav)
 
                 if (postViewModel.wantsToMarkAsSensitive) {