Add sync engine, web UI, Docker setup, and tests

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

import_to_outline.sh

@@ -143,6 +143,6 @@ docker run --rm --network domnet \
     -v "$WORK_DIR:/work" \
     -w /work \
     python:3.11-slim \
-    bash -c "pip install -qqq requests 2>/dev/null && python3 outline_import.py $CLI_ARGS"
+    bash -c "pip install -qqq requests tqdm 2>/dev/null && python3 outline_import.py $CLI_ARGS"
 
 echo ""