Add gitignore, clean large files from history

.gitignore

+# PCAP files (large captures)
+*.pcap
+**/pcaps_input/
+**/pcaps_output/
+
+# Node
+**/node_modules/
+**/frontend/dist/
+
+# Spark jars (dependencies, not source)
+**/spark-jars/*.jar
+
+# Output / generated data
+**/output/
+**/data/
+
+# Models
+**/models/**/*.zip
+**/models/**/*.parquet
+**/models/*_model/
+
+# Python
+__pycache__/
+*.pyc
+.venv/
+venv/
+
+# Hadoop data
+**/namenode-data/
+**/datanode-data/
+
+# OS / logs
+.DS_Store
+*.log