security: Remove DerivedData and build artifacts from repo, add .gitignore

DerivedData/ (371 files) and build/ (554 files) were committed to the
public repo. This removes all build artifacts from tracking and adds a
comprehensive .gitignore to prevent them from being committed again.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kochj23

.DS_Store

@@ -0,0 +1,55 @@
+# Xcode
+DerivedData/
+build/
+*.xcodeproj/project.xcworkspace/
+*.xcodeproj/xcuserdata/
+*.xcworkspace/xcuserdata/
+xcuserdata/
+*.pbxuser
+\!default.pbxuser
+*.mode1v3
+\!default.mode1v3
+*.mode2v3
+\!default.mode2v3
+*.perspectivev3
+\!default.perspectivev3
+*.xccheckout
+*.moved-aside
+*.xcuserstate
+*.hmap
+*.ipa
+*.dSYM.zip
+*.dSYM
+timeline.xctimeline
+playground.xcworkspace
+*.xcscmblueprint
+
+# Swift Package Manager
+.build/
+Packages/
+Package.resolved
+
+# CocoaPods
+Pods/
+Podfile.lock
+
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+._*
+.Spotlight-V100
+.Trashes
+
+# Secrets
+*.p12
+*.cer
+*.mobileprovision
+secrets.json
+credentials.json
+.env
+.env.*
+config.plist
+
+# Archives
+*.xcarchive