Duplicate menu entries and inconsistent Test Plan naming during merge in JMeter 5.6.3

### Expected behavior

**Menu entries should be consistent and non‑duplicated.**
• File menu should contain file‑level actions.
• Edit menu should contain node‑level actions.
• Merge behavior should be predictable: either always preserve the current Test Plan name or always adopt the merged file’s name, regardless of selected node.

### Actual behavior

**1. Inconsistent Test Plan naming after merge**
- If Test Plan node is selected: merged file contents are added, but the Test Plan name remains from the current plan (e.g., Test Plan A).
- If a Thread Group node is selected: merged file contents are added, but the Test Plan name changes to the merged file’s name (e.g., Test Plan B).
- This behavior is identical whether using File → Merge… or Edit → Merge….

**2. - Additional observation (not part of reproduction steps)**
- Duplicate menu entries exist: File → Merge… and Edit → Merge…, File → Open… and Edit → Open…, File → Save Selection As… and Edit → Save Selection As….
- These perform the same action, which may confuse users.

### Steps to reproduce the problem

1. Open JMeter 5.6.3.
2. Create Test Plan A with a Thread Group and HTTP Request.
3. Save another file as Test Plan B with a Thread Group and HTTP Request.
4. Select the Test Plan node in Test Plan A.
5. Use File → Merge… (or Edit → Merge…) to merge Test Plan B.
6. Result: Test Plan name remains Test Plan A.
7. Select the Thread Group node in Test Plan A.
8. Use File → Merge… (or Edit → Merge…) to merge Test Plan B.
9. Result: Test Plan name changes to Test Plan B.

### JMeter Version

5.6.3

### Java Version

java version "25.0.1" 2025-10-21 LTS Java(TM) SE Runtime Environment (build 25.0.1+8-LTS-27) Java HotSpot(TM) 64-Bit Server VM (build 25.0.1+8-LTS-27, mixed mode, sharing)

### OS Version

OS Version: Windows 10 Pro, Version 22H2 (OS Build 19045.6216)