fix: remove Windows Debug build from LLVM matrix

LLVM_USE_SANITIZER=Address is not supported on Windows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 16bit-ykiko

.github/workflows/build-llvm.yml

@@ -14,9 +14,6 @@ jobs:
       matrix:
         include:
           # ── Native builds ──────────────────────────────────────────────
-          - os: windows-2025
-            llvm_mode: Debug
-            lto: OFF
           - os: windows-2025
             llvm_mode: RelWithDebInfo
             lto: OFF