feat: deduplicate sidebar signal counts by source URL

feat: deduplicate knowledge graph nodes by source URL

feat: deduplicate top-3 overview signals by source URL

test: add test_graph_engine, test_agents, test_summary_engine, test_integration_pipeline

fix(tests): repair broken pipeline tests and delete stale q2/ suite

chore: add core/ modules, archive legacy code, update gitignore

Fix all 5 autopsy defects: create sentinel.py, enable WAL mode, fix reports dir, purge 18 redundant files

Initial commit for Fendt PESTEL-EL Sentinel Dashboard