feat: make the road event map follow the app's dark theme

osmdroid's MAPNIK tiles are always light, so in dark mode the bright map
clashed with the UI and light overlays. Apply a night-mode colour-matrix
filter to the tiles overlay when MaterialTheme.colorScheme.isLight is
false (lightness-inverted + desaturated for a clean dark-grey map, not a
plain invert that turns forests magenta). Light theme keeps normal tiles.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017tYbcy4UGWxqQbcycyL7Yd

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/location/LocationPreviewMap.kt

@@ -20,10 +20,13 @@
  */
 package com.vitorpamplona.amethyst.ui.note.creators.location
 
+import android.graphics.ColorFilter
+import android.graphics.ColorMatrixColorFilter
 import android.graphics.drawable.BitmapDrawable
 import android.view.MotionEvent
 import androidx.compose.foundation.layout.aspectRatio
 import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.remember
@@ -35,6 +38,7 @@ import androidx.compose.ui.viewinterop.AndroidView
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleEventObserver
 import androidx.lifecycle.compose.LocalLifecycleOwner
+import com.vitorpamplona.amethyst.ui.theme.isLight
 import org.osmdroid.config.Configuration
 import org.osmdroid.tileprovider.tilesource.TileSourceFactory
 import org.osmdroid.util.GeoPoint
@@ -45,6 +49,38 @@ import org.osmdroid.views.overlay.Marker
 /** Default close-up zoom for a single pinned location (street-level). */
 private const val DEFAULT_ZOOM = 16.0
 
+/**
+ * Night-mode filter for the (always-light) MAPNIK tiles so the map follows the
+ * app theme. Inverts lightness while desaturating, which reads as a clean dark
+ * grey map — unlike a plain colour invert, which turns forests magenta and
+ * water orange.
+ */
+private val NIGHT_TILE_FILTER: ColorFilter =
+    ColorMatrixColorFilter(
+        floatArrayOf(
+            -0.6f,
+            -0.4f,
+            -0.4f,
+            0f,
+            255f,
+            -0.4f,
+            -0.6f,
+            -0.4f,
+            0f,
+            255f,
+            -0.4f,
+            -0.4f,
+            -0.6f,
+            0f,
+            255f,
+            0f,
+            0f,
+            0f,
+            1f,
+            0f,
+        ),
+    )
+
 /**
  * A small OpenStreetMap (osmdroid) preview centered on [latitude]/[longitude]
  * with a single pin at that point.
@@ -75,6 +111,7 @@ fun LocationPreviewMap(
 ) {
     val context = LocalContext.current
     val lifecycleOwner = LocalLifecycleOwner.current
+    val darkTheme = !MaterialTheme.colorScheme.isLight
 
     val markerIcon =
         remember(pinColor, pinEmoji) {
@@ -134,6 +171,9 @@ fun LocationPreviewMap(
             map.controller.setZoom(zoom)
             map.controller.setCenter(point)
 
+            // Follow the app theme: dim the bright MAPNIK tiles in dark mode.
+            map.overlayManager.tilesOverlay.setColorFilter(if (darkTheme) NIGHT_TILE_FILTER else null)
+
             map.overlays.removeAll { it is Marker }
             val marker =
                 Marker(map).apply {