Merge success animation + auto-return to landing page; bump to 3.0

On a successful merge, show a brief full-screen green checkmark animation
('Merged'), then automatically pop the PR detail view back to the landing
page. MergeSheet now calls an onSuccess callback; PRDetailView shows the
overlay and dismisses after ~1.2s. Bump to 3.0.

GiteaPR/Detail/Sheets.swift

@@ -65,6 +65,9 @@ struct MergeSheet: View {
     @ObservedObject var vm: PRDetailViewModel
     @Environment(\.dismiss) private var dismiss
     @State private var method = "merge"
+    /// Called when the merge succeeds, so the parent can show the success
+    /// animation and pop back to the landing page.
+    var onSuccess: () -> Void = {}
 
     private let methods = [("merge", "Create merge commit"),
                            ("rebase", "Rebase and merge"),
@@ -129,7 +132,10 @@ struct MergeSheet: View {
     private func performMerge() {
         Task {
             let success = await vm.merge(method: method)
-            if success { dismiss() }
+            if success {
+                dismiss()
+                onSuccess()
+            }
         }
     }
 }