merge trails function added (#627)

* merge trails function added

* fix conflict resolve issues

* avoid incorrect authorship when merging trail comments

* require edit access for all selected trails before merge

* fix likes checkbox binding in trail merge modal

* improve error handling

* require editable target and deletable sources for merge

* avoid duplicate trail fetch during merge

* prevent duplicate likes when merging trails

* check photo download responses during trail merge

* add merge completion toast notifications

* cleanup

* small fixes

* move merge code to backend, option to merge single trail selection with similar one, automatic merge for integrations add as option, maintenance page to find and merge similar trails added

* fix build error

* fix

* docu, beautifying, refactoring

---------

Co-authored-by: Flomp <Flomp@users.noreply.github.com>

web/src/lib/components/trail/trail_info_panel.svelte

@@ -1,7 +1,8 @@
 <script lang="ts">
     import { goto } from "$app/navigation";
+    import { page } from "$app/state";
     import Tabs from "$lib/components/base/tabs.svelte";
-    import TrailDropdown from "$lib/components/trail/trail_dropdown.svelte";
+    import TrailDropdown, { type MergeResult } from "$lib/components/trail/trail_dropdown.svelte";
     import { Comment } from "$lib/models/comment";
     import type { Trail } from "$lib/models/trail";
 
@@ -269,6 +270,21 @@
         summitLogs.set(newSummitLogList);
     }
 
+    function handleTrailMerge(result: MergeResult) {
+        if (!trail.id || !result.deletedTrailIds.includes(trail.id)) {
+            return;
+        }
+
+        const targetHandle = handleFromRecordWithIRI(result.targetTrail);
+        const targetPath =
+            mode === "map"
+                ? `/map/trail/${targetHandle}/${result.targetTrail.id}`
+                : `/trail/view/${targetHandle}/${result.targetTrail.id}`;
+
+        const search = page.url.searchParams.toString();
+        goto(search ? `${targetPath}?${search}` : targetPath);
+    }
+
     async function markTrailAsCompleted() {
         trail.completed = true;
         const updatedTrail: Trail = { ...trail };
@@ -430,6 +446,7 @@
                         trails={new Set<Trail>([trail])}
                         onDelete={() =>
                             history.length ? history.back() : goto("/trails")}
+                        onMerge={handleTrailMerge}
                         {mode}
                     ></TrailDropdown>
                 </div>