Add optional DuckDB debug log database with typed schema

New --debug-db flag writes the redacted debug record stream to a DuckDB database alongside or instead of the NDJSON --debug-file. Frequent type-stable attributes are promoted to typed columns; the complete record remains in attrs JSON. libduckdb is dlopen'ed at runtime (build tag duckdb, Arch optdepends) so the reader runs unchanged without it. v1 databases upgrade in place on append.

.gitignore

@@ -17,3 +17,10 @@ __pycache__/
 /distro-packages/Arch-Linux/cthulhu-git/*/
 
 /cmd/cthulhu/cthulhu
+
+# Local tooling output and debug artifacts (never fixtures)
+/graphify-out/
+/*.log
+*.duckdb
+*.duckdb.wal
+/test.db*