Issue #3613068: Remove stale "(preview)" framing from by-role dashboard

Jérôme Tchaniarequested to merge
issue/ai_metering-3613068:3613068-remove-byrole-preview-copy into 1.0.x

Closes #3613068

The by-role dashboard is a finished, fully working feature (aggregation, pagination, export, CTA), but the menu item, hub page card, on-page banner, and controller docblock still labeled it "(preview)" / "demo-only" / "roadmap". Replaces all five surfaces with a plain description matching the rest of the module's admin pages. Leaves the unrelated "preview" wording on the personal-usage-tab link in the hub template untouched (different feature, legitimate ongoing concept).

Tests: existing 241 tests unaffected, full suite green.

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