Add .gitattributes to keep local application.yml and api.ts and helper script

Author: Warren-SJ

.gitattributes

@@ -0,0 +1,3 @@
+# Keep local versions of these files when merging from main
+backend/src/main/resources/application.yml merge=ours
+frontend/lib/api.ts merge=ours

scripts/setup-local-branch.ps1

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+# Setup script for local branch merge driver
+# Run this after checking out the 'local' branch to configure the merge driver locally.
+
+# Ensure we're in repo root
+Set-Location -Path $PSScriptRoot\..\
+
+# Configure the 'ours' merge driver locally to always keep our version
+git config --local merge.ours.driver true
+
+Write-Host "Configured merge.ours.driver true in local git config"
+Write-Host "Remember to commit .gitattributes on branch 'local' with your local-only files changed."