Fix build regressions when main repo has build artifacts

[Pterjudin]

• Phase 1: Expand rsync exclusions to exclude all build artifacts (out-build, out-vscode-min, .cache, dist, *.tsbuildinfo, react/out)
• Phase 2: Add post-copy cleanup to remove any artifacts that slip through
• Phase 3: Add source state verification (warn only, non-blocking) for uncommitted changes and missing package-lock.json
• Phase 4: Force clean node_modules before npm install to prevent contamination
• Phase 5: Add file integrity check to verify critical files exist after copy
• Phase 6: Normalize timestamps to prevent build cache issues

All phases tested and validated. This ensures that if main repo runs without issues, builder will also build successfully.