feat(loyalty): add Chart.js visualizations to analytics page

Wire the Phase 7 analytics API endpoints into the store analytics
page with interactive visualizations:

- Revenue chart (Chart.js bar+line combo): monthly points earned as
  bars + active customers as line overlay with dual Y axes.
- At-risk members panel: ranked list of churning cards showing
  customer name and days inactive, with count badge.
- Cohort retention table: enrollment month rows × M0-M5 retention
  columns with color-coded percentage cells (green >60%, yellow
  >30%, red <30%).

Chart.js loaded on-demand via existing CDN loader with local fallback.
Data fetched in parallel via Promise.all for the 3 analytics endpoints.
All sections gracefully degrade to "not enough data" message when empty.

7 new i18n keys (EN only — FR/DE/LB translations to be added).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/locales/en.json

@@ -801,7 +801,15 @@
       "quick_actions": "Quick Actions",
       "open_terminal": "Open Terminal",
       "view_members": "View Members",
-      "view_program": "View Program"
+      "view_program": "View Program",
+      "revenue_title": "Points & Customers",
+      "at_risk_title": "At-Risk Members",
+      "cards_at_risk": "members at risk of churn",
+      "no_at_risk": "All members are active!",
+      "cohort_title": "Cohort Retention",
+      "cohort_month": "Enrollment Month",
+      "cohort_enrolled": "Enrolled",
+      "no_data_yet": "Not enough data yet. Analytics will appear as customers enroll and transact."
     },
     "program": {
       "title": "Loyalty Program",