fix(frontend): resolve MEMMY-316, MEMMY-317 and MEMMY-318

[Memtensor-AI]

Summary

• MEMMY-318: keep the memory-page header below the Windows native title-bar overlay so the refresh button remains clickable.
• MEMMY-317: keep the memory detail drawer below the same overlay so its close button no longer conflicts with the native window close control.
• MEMMY-316: clear deleted model preset references from both BYOK and account assignments so model deletion persists without a Backend validation error.
• Add regression coverage for all three defects, including a real Backend catalog persistence test for model deletion.

Verification

• Project Harness Standard: passed
• Frontend lint: passed
• Frontend typecheck: passed
• Frontend workspace tests: passed
• Desktop UI Vitest assertions: passed
• Targeted model-workspace tests: 26 passed
• Targeted style-alignment tests: 14 passed

Base

Based on upstream main at v1.1.0 (b4c37f7).

[Memtensor-AI]

已拆分为三个独立、以 v1.1.1 为目标分支的 Harness Bugfix Lite PR：MEMMY-318 #302、MEMMY-317 #303、MEMMY-316 #304。本混合 PR 不再使用。