ux(frontend/recs): action-box summary shows financial range, not selected/visible counts

[cristim]

Problem

The bottom-action-box summary text reads (1 selected of 1 cells visible) (recommendations.ts:1869). The selected-vs-visible count
is the least useful information at this point — the user can already
see selection state from row checkboxes, and the visible count is
in the filter status bar.

What would be more useful

Surface the financial summary of the current action target:
"$N–$M monthly savings, $K upfront across J cells", same shape as the
"Recommended range" banner that's about to go away (#…). The user is
about to commit to a purchase / plan; the action-box summary is
prime real estate for the dollar figures they're authorising.

Acceptance criteria

• Summary text shows: current action target's pageLevelRange
  (savings range + upfront range + cell count).
• Falls back to a neutral prompt when no rows visible / no
  selection (matches the disabled-button state).
• Updates on every list rerender (sort, filter, selection
  change).
• Existing test bottom action box selection summary reflects current selection (Bundle B) updated to assert the new shape.