Add error handling for empty concept generation in automated workflow

[Copilot]

Addresses review feedback from #79: the commit step didn't handle cases where all concepts are filtered as "weak", potentially causing silent failures.

Changes

Added explicit check for staged changes before commit:

git add knowledge-database/concepts
if git diff --cached --quiet; then
  echo "⚠️ No concept files generated"
  exit 1
fi
git commit -m "..."

The workflow now fails fast with a clear error message when no concepts are generated, rather than continuing with undefined behavior.

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