feat: geohash bookmarks (iOS parity) (#410)

* Geohash bookmarks (iOS parity):
- Add GeohashBookmarksStore (persist bookmarks + friendly names)
- Integrate bookmark toggle into LocationChannelsSheet (nearby + bookmarked sections)
- Add header toggle for current geohash bookmark
- Sample counts for union of nearby + bookmarks while sheet open
- Add Geohash.decodeToBounds() to support friendly name resolution
- Fix coroutine usage and Gson type inference issues

* fix UI

* clear bookmarks on triple tap

* adjust icons

---------

Co-authored-by: callebtc <93376500+callebtc@users.noreply.github.com>

app/src/main/java/com/bitchat/android/ui/ChatViewModel.kt

@@ -719,8 +719,14 @@ class ChatViewModel(
         // Clear all notifications
         notificationManager.clearAllNotifications()
         
-        // Clear Nostr/geohash state, keys, connections, and reinitialize from scratch
+        // Clear Nostr/geohash state, keys, connections, bookmarks, and reinitialize from scratch
         try {
+            // Clear geohash bookmarks too (panic should remove everything)
+            try {
+                val store = com.bitchat.android.geohash.GeohashBookmarksStore.getInstance(getApplication())
+                store.clearAll()
+            } catch (_: Exception) { }
+
             geohashViewModel.panicReset()
         } catch (e: Exception) {
             Log.e(TAG, "Failed to reset Nostr/geohash: ${e.message}")