Selecting a rule now shows the transactions it would alter, so a subset can be
ticked and applied rather than trusting a bulk run. The apply step takes explicit
transaction ids (the existing bulk apply_rule path), so what you tick is exactly
what changes - a rule whose conditions are too broad cannot reach further than
the preview showed.
Matches are split into 'would change' and 'already correct'. A merchant
normalisation rule matching 400 rows where 380 already hold the right value is 20
changes and 380 rows of noise; only the 20 are listed.
Preview is offered for every rule including manual_only quick actions, which
previously had no way to see their reach at all. A rule with no conditions
matches every transaction - that is how apply already behaves, so the preview
reports it prominently rather than hiding it.
Applies still snapshot to rule_apply_runs, so they remain revertable.
