feat(route-builder): match dropped images to imported hash-only waypoints

After a GPX import the image-anchor waypoints carry just their
content hash (no thumbnail). Drop the source JPEGs into the same
image dropzone and they're now hashed and matched against existing
waypoints first — on a hit, the thumbnail + full-resolution cache
are patched onto the matched row instead of creating a duplicate
waypoint marker on the map.

A blue 'Bildvorschau ergänzt' status row + contextual hint at the
top of the dropzone ('N Bild-Wegpunkte warten auf eine Vorschau —
Originale hier ablegen') makes the round-trip workflow discoverable.

Existing fresh-upload behaviour (new image → new chronologically-
inserted waypoint with EXIF GPS) is unchanged for any image whose
hash isn't already known to the builder.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.77.0",
+	"version": "1.77.1",
 	"private": true,
 	"type": "module",
 	"scripts": {