Summary

Add a new On-Demand Monthly Cost column to the recommendations table on the Recommendations page so users can see the unsubsidised monthly cost alongside the discounted Monthly Cost and Effective % columns.

Why

Today the table shows:

• Monthly Cost — recurring discounted cost
• Savings — monthly delta vs on-demand
• Effective % — savings as a fraction of the equivalent on-demand monthly

…but never surfaces the on-demand baseline directly. Users routinely want to answer "what would I pay without this commitment?" and currently have to do the arithmetic in their head:

on_demand_monthly = monthly_cost + savings + (upfront_cost / (term_years * 12))

This identity is already implemented in frontend/src/recommendations.ts (see the doc comment for effectiveSavingsPct at L388–415) — the value exists, it's just not displayed.

Scope

• New column key: on_demand_monthly (display label "On-Demand Monthly").
• Renders formatCurrency(...) for non-null monthly_cost; renders — when monthly_cost is null (provider didn't return a recurring breakdown — same convention as the existing Monthly Cost column at L1510).
• Sortable + filterable like the other numeric columns:
  • Add to numericColumns near L189–198 (return Number.POSITIVE_INFINITY when null so null rows sort to the end consistently with monthly_cost).
  • Add to the column-header label map at L485-ish.
  • Add to the cell-value resolver around L614–619 (return Number.NaN for null so numeric filter predicates don't match = 0 spuriously).
  • Add to the column orderings at L646 and L1481.
• Add a unit test covering: null monthly_cost → —, non-null with savings + amortized upfront → matches monthly_cost + savings + (upfront_cost/(term*12)).

Out of scope

• The cost-period selector (hourly / daily / monthly / yearly) is filed as a separate issue and will fold this column into its scaling once both ship.
• No backend change required — pure frontend derivation.

Acceptance criteria

• Column renders correctly for AWS, Azure, GCP rows where monthly_cost is non-null.
• Renders — (em-dash) when monthly_cost is null.
• Sort by on_demand_monthly (asc + desc) works; null rows sort to the end.
• Numeric filter predicates (>, <, =) on the column match the same semantics as monthly_cost.
• Unit test added in frontend/src/__tests__/recommendations.test.ts.
• No regressions in existing column ordering / sort / filter tests.