refactor(portal): delete data/customers.ts fixture entirely

Replace the last two holdouts: the dashboard partner-identity fallback now uses the real useMe().partner name, and the decorative MRR sparkline (dashboard + reports) moves to a generated useMrrTrendline() — deterministic, clearly placeholder-only, until a daily MRR-snapshot job exists. Removes the dead sparkLast/sparkTrendPct vars. The data/customers.ts fixture module is now fully deleted; the partner portal carries no mock business data.

apps/portal/data/customers.ts

@@ -1,30 +0,0 @@
-// Remaining partner fixtures. `partner` (dashboard fallback identity) and
-// `partnerMrrSparkline` (decorative dashboard/reports sparkline) are the last
-// two holdouts — kept until the dashboard partner header and a real historical
-// MRR series replace them. The customer list now comes from /api/partner/tenants.
-
-export const partner = {
-  id: 'p-nordicmsp',
-  name: 'NordicMSP',
-  domain: 'nordicmsp.dk',
-  contact: 'Anne Baslund',
-  email: 'partners@nordicmsp.dk',
-  marginPct: 20,
-  customers: 8,
-  brandColor: '#3F6BFF',
-  founded: '2024',
-}
-
-// 90-day MRR sparkline · matches the synthetic generator at partner-screens.jsx:198.
-// Deterministic seeded values (no Math.random calls each render).
-export const partnerMrrSparkline = [
-  38580, 38980, 39520, 40180, 40720, 41080, 41420, 41820, 42100, 42460,
-  42820, 43240, 43620, 43980, 44320, 44660, 44960, 45280, 45680, 46020,
-  46300, 46580, 46880, 47220, 47540, 47820, 48160, 48420, 48760, 49080,
-  49420, 49680, 50020, 50360, 50640, 50920, 51180, 51460, 51720, 51980,
-  52220, 52480, 52720, 52960, 53180, 53420, 53620, 53860, 54080, 54260,
-  54440, 54620, 54780, 54940, 55080, 55180, 55280, 55360, 55440, 55510,
-  55570, 55610, 55650, 55670, 55690, 55700, 55710, 55720, 55730, 55740,
-  55745, 55748, 55750, 55750, 55750, 55750, 55750, 55750, 55750, 55750,
-  55750, 55750, 55750, 55750, 55750, 55750, 55750, 55750, 55750, 55750,
-]