feat(analysis): add trend charts to the Analysis page

The Analysis page only showed KPI numbers. Add two real time-series and render
them as dependency-free bar charts (matching components/chat/sparkline.tsx):

- backend: GET /api/analytics now returns `trends.patientsByMonth` (new patients
  per month over the last 6 months) and `trends.appointmentsByWeekday`
  (appointments per day for the current week), bucketed in JS from one query each.
- frontend: new components/analysis/bar-chart.tsx and two chart sections on the
  Analysis view (Patient growth, Appointments this week), with i18n keys.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/types/analytics.ts

@@ -1,3 +1,6 @@
+// A single bar/point in a time-series chart (e.g. one month or one weekday).
+export type TrendPoint = { label: string; count: number };
+
 // Server-computed clinic analytics returned by GET /api/analytics. All figures
 // are aggregates over the active clinic's real data (no fabricated financials).
 export type Analytics = {
@@ -20,4 +23,10 @@ export type Analytics = {
     open: number;
     done: number;
   };
+  // Time-series for charts: new patients over the last 6 months, and
+  // appointments per day across the current week.
+  trends: {
+    patientsByMonth: TrendPoint[];
+    appointmentsByWeekday: TrendPoint[];
+  };
 };