feat(convert): integrate process metrics into JSON and SQLite converters

- add process_metrics function to record peak RSS and CPU time
- update JSON converter to include metrics in completion marker
- modify SQLite converter to utilize new metrics for performance tracking
- enhance storage size updates with locking mechanism for concurrent access

common/pg.py

@@ -0,0 +1,16 @@
+"""PostgreSQL DSN access (docs/rules/code-config-yaml.md section 3).
+
+The DSN comes from the TRIBO_PG_DSN environment variable and is read ONLY
+here. It may embed a password: never log it, never hardcode it, never
+commit it - log host/database names at most.
+"""
+
+from __future__ import annotations
+
+import os
+
+DEFAULT_DSN = "postgresql://postgres@localhost:5432/tribo"
+
+
+def get_dsn() -> str:
+	return os.environ.get("TRIBO_PG_DSN", DEFAULT_DSN)