Consolidate company admin screens: health badge on list, tabbed detail page

Companies/Index:
- Added Health badge column (Healthy / At Risk / Critical / Never Active)
  with the numeric score in a tooltip; computed from the same signals as
  CompanyHealth/Index using the new shared CompanyHealthHelper

Companies/Details:
- Converted flat card layout to five tabs: Overview, Users, Subscription,
  Onboarding, Health; URL hash is preserved so the active tab survives
  page refresh and back navigation
- Subscription tab shows plan/status/dates with an expiry countdown and a
  "Manage Subscription & Features" button to the full Manage page
- Onboarding tab shows wizard completion, milestone progress bar, and
  first-activity dates (previously only on the standalone page)
- Health tab shows score gauge, risk badge, and individual risk signals
  with a link through to the full CompanyHealth dashboard
- JS moved to wwwroot/js/companies-details.js (avoids inline-script failures)

Infrastructure:
- Extracted ComputeHealth / ToRiskLevel / ChurnRisk to CompanyHealthHelper.cs
  (same Controllers namespace); CompanyHealthController delegates to it
- CompanyCountSummary extended with Jobs30Counts, Jobs90Counts, LastLoginDates
  (3 extra GROUP BY queries scoped to the current page IDs, not all companies)
- CompanyListDto gains HealthScore, HealthRisk, LastLoginDate

Navigation:
- Removed "Onboarding Progress" hub card from People & Activity; the data
  is now surfaced directly on the Companies/Details Onboarding tab

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/PlatformAdminController.cs

@@ -48,7 +48,6 @@ public class PlatformAdminController : Controller
             Card("Platform Users", "Manage SuperAdmin accounts and review platform-user access details.", "PlatformUsers", "Index", "bi-people-fill", "Daily", SubtleBadge("primary")),
             Card("User Activity", "Review cross-tenant usage history, filters, and behavioral trends.", "UserActivity", "Index", "bi-person-lines-fill", "Review", SubtleBadge("success")),
             Card("Online Now", "Check who is currently active in the application right now.", "UserActivity", "Online", "bi-broadcast-pin", "Live", SubtleBadge("success")),
-            Card("Onboarding Progress", "Track which companies are still working through setup and activation milestones.", "OnboardingProgress", "Index", "bi-rocket-takeoff", "Support", SubtleBadge("warning")),
             Card("Platform Notifications", "Review platform-level in-app notifications and operational follow-ups.", "PlatformNotifications", "Index", "bi-bell", "Monitor", SubtleBadge("info"))
         }
     };