row_estimate came from pg_class.reltuples, which is -1 for tables that
have never been ANALYZEd (the common case on a fresh/small DB), so the
admin table list showed -1 for every table — meaningless.
Replace row_estimate with row_count + row_count_estimated:
- total_size < 100MB: SELECT count(*) (real value, cost negligible on
small tables; identifier quoted via PG escaping to stay injection-safe)
- total_size >= 100MB: fall back to reltuples estimate, flagged so the UI
can prefix with ~
Frontend now shows real counts (1/2/14...) for small tables and ~N for
large ones; header copy updated to reflect the mixed source.