Bug: shared DataTable footer renders "Showing all 1 projects" / "Showing all 1 agents" — {entity} never singularizes

[yannickmonney]

Problem

The shared DataTable footer key pagination.showingAll = "Showing all {count} {entity}" interpolates a fixed lowercase-plural entity label (per the prop's own doc: 'Lowercase plural entity label (e.g., "websites")'), so any table with exactly one row reads "Showing all 1 projects" / "Showing all 1 agents". #2053 fixed this class on other strings; the shared footer instance survived (also noted in passing on #2348).

Current behaviour

Projects list with one project (every fresh org): footer status reads "Showing all 1 projects" (2026-07-11, main @ 94ef84e). Same pattern on any single-row DataTable page (agents, contacts, …).

Code pointers

• messages/en.json:1818 — "showingAll": "Showing all {count} {entity}"
• app/components/ui/data-table/data-table.tsx:166,1169 — plural-only entity prop + the t('pagination.showingAll', …) call

Proposed change

Move the entity noun into ICU plural form — either per-entity {count, plural, one {…} other {…}} message keys, or have callers pass singular+plural labels the footer selects between.

Acceptance criteria

• One-row tables read "Showing all 1 project" (correctly pluralized in every locale)
• All DataTable consumers (projects, agents, contacts, websites, …) covered by the same fix

Related: #2053, #2348.