Merge icon, delete-branch-after-merge setting, floating tab bar; bump to 2.0

- Merge button: use the proper SF Symbol 'arrow.triangle.merge' instead of
  the download icon 'arrow.down.circle'.
- Add a Settings toggle 'Delete branch after merge'. When on, the merge call
  passes delete_branch_after_merge=true and the head branch is deleted after
  a successful merge (best-effort).
- PR detail bottom tab bar: floating capsule style (regularMaterial + shadow)
  like the latest iOS tab bars, instead of a full-width bar.
- Bump to 2.0.

GiteaPR/Networking/GiteaClient.swift

@@ -211,12 +211,23 @@ struct GiteaClient {
     }
 
     func merge(owner: String, repo: String, number: Int,
-               method: String) async throws {
-        struct Body: Encodable { let Do: String } // 'Do' = merge method: merge|rebase|squash
+               method: String, deleteBranchAfterMerge: Bool) async throws {
+        struct Body: Encodable {
+            let Do: String          // merge|rebase|squash
+            let delete_branch_after_merge: Bool
+        }
         _ = try await request(
             "repos/\(owner)/\(repo)/pulls/\(number)/merge",
             method: "POST",
-            body: try JSONEncoder().encode(Body(Do: method)))
+            body: try JSONEncoder().encode(Body(Do: method,
+                                                 delete_branch_after_merge: deleteBranchAfterMerge)))
+    }
+
+    /// Delete a branch (used after merging when the setting is enabled).
+    func deleteBranch(owner: String, repo: String, branch: String) async throws {
+        let encoded = branch.addingPercentEncoding(withAllowedCharacters: .urlPathAllowed) ?? branch
+        _ = try await request("repos/\(owner)/\(repo)/branches/\(encoded)",
+                              method: "DELETE")
     }
 
     func setState(owner: String, repo: String, number: Int,