Use max compression for sidecar zips to reduce upload size

zip -9 on Linux, 7z -mx=9 on Windows. Compression takes longer but
produces smaller files which upload faster over the network.

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

.gitea/workflows/build-sidecar-windows.yml

@@ -64,7 +64,7 @@ jobs:
       - name: Package sidecar (CUDA)
         shell: powershell
         run: |
-          7z a -tzip -mx=5 sidecar-windows-x86_64-cuda.zip .\dist\local-transcription-backend\*
+          7z a -tzip -mx=9 sidecar-windows-x86_64-cuda.zip .\dist\local-transcription-backend\*
 
       - name: Build sidecar (CPU)
         shell: powershell
@@ -76,7 +76,7 @@ jobs:
       - name: Package sidecar (CPU)
         shell: powershell
         run: |
-          7z a -tzip -mx=5 sidecar-windows-x86_64-cpu.zip .\dist\local-transcription-backend\*
+          7z a -tzip -mx=9 sidecar-windows-x86_64-cpu.zip .\dist\local-transcription-backend\*
 
       - name: Upload to sidecar release
         shell: powershell