feat(bench): add SQLite and PostgreSQL wrappers for benchmark queries

- implement SQLite and PostgreSQL wrappers to execute benchmark queries
- update README to reflect task 09 as implemented
- enhance storage size updates to handle (format, variant) replacements
- clarify benchmarking methodology for remote PostgreSQL setup

docs/rules/bench-methodology.md

@@ -82,6 +82,15 @@ invalidates everything downstream.
   pass is therefore SKIPPED and marked as such in results and report -
   never approximated by a fake (e.g. file re-copy tricks) without a
   rules update describing the method.
+- **PostgreSQL is remote on this setup** (dedicated DB host on the LAN),
+  so spec 09's backend-PID sampling via `pg_stat_activity` + psutil is
+  impossible - psutil cannot attribute a remote process. Instead the
+  runner records (a) client-side child metrics exactly like every other
+  format (wall times therefore include LAN round-trips - stated in the
+  report), (b) best-effort Prometheus / node_exporter host CPU/RAM
+  windows per PG cell and for the whole session (`TRIBO_PROM_URL`), and
+  (c) best-effort `pg_stat_statements` per-query session deltas
+  (server-side execution time and buffer traffic).
 - Quiesce the machine during measured runs (no parallel pipeline tasks,
   no background loads); the runner runs cells sequentially by design.