feat(geohash): add in-app Geohash Picker (#363)

* feat(geohash): add in-app Geohash Picker map with quadrant drill-down and Activity integration

- New GeohashPickerActivity hosting a WebView with Leaflet-based picker
- Adds map icon next to custom geohash input in LocationChannelsSheet
- Picker allows quadrant selection and subquadrant drill-down; returns selected geohash
- Register activity in AndroidManifest

perf(picker): improve map performance and correctness
- Use LayerGroup and clearLayers() on redraw to avoid stale overlays
- Use Leaflet canvas renderer for rectangles to reduce DOM and improve perf
- Make labels non-interactive and pointer-events: none to avoid gesture overhead
- Fix initial mega-label artifact by grouping and clearing labels with cells

chore: add asset geohash_picker.html with minimal geohash helpers (bounds/encode/adjacent)

* remove accidentally committed submodule.

* fix some issues

* better geohash labels on map

* design wip

* countries green

* wip

* geohashpicker: pan + zoom; start from current geohash channel

* better ui

* ui elements

* nice

* readability

---------

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

app/src/main/AndroidManifest.xml

@@ -41,6 +41,12 @@
         android:supportsRtl="true"
         android:theme="@style/Theme.BitchatAndroid"
         tools:targetApi="31">
+        <activity
+            android:name=".ui.GeohashPickerActivity"
+            android:exported="false"
+            android:theme="@style/Theme.BitchatAndroid"
+            android:screenOrientation="portrait"
+            android:windowSoftInputMode="adjustResize" />
         <activity
             android:name=".MainActivity"
             android:exported="true"