feat: trends report — global flow + by category with view toggle (#72)

- Flesh out ReportsTrendsPage with internal subview toggle
  (global / byCategory) and ViewModeToggle (storage key reports-viewmode-trends)
- Reuse existing MonthlyTrendsChart/Table and CategoryOverTimeChart/Table
  without modification; wire them through useTrends + useReportsPeriod so the
  URL period is respected
- Add reports.trends.subviewGlobal / subviewByCategory keys in FR + EN

Fixes #72

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

src/i18n/locales/en.json

@@ -399,6 +399,10 @@
       "categoryZoom": "Category Analysis",
       "categoryZoomDescription": "Zoom in on a single category"
     },
+    "trends": {
+      "subviewGlobal": "Global flow",
+      "subviewByCategory": "By category"
+    },
     "highlights": {
       "balances": "Balances",
       "netBalanceCurrent": "This month",

src/i18n/locales/fr.json

@@ -399,6 +399,10 @@
       "categoryZoom": "Analyse par catégorie",
       "categoryZoomDescription": "Zoom sur une catégorie"
     },
+    "trends": {
+      "subviewGlobal": "Flux global",
+      "subviewByCategory": "Par catégorie"
+    },
     "highlights": {
       "balances": "Soldes",
       "netBalanceCurrent": "Ce mois-ci",

src/pages/ReportsTrendsPage.tsx

@@ -1,11 +1,116 @@
+import { useState, useCallback } from "react";
 import { useTranslation } from "react-i18next";
+import { Link } from "react-router-dom";
+import { ArrowLeft } from "lucide-react";
+import PeriodSelector from "../components/dashboard/PeriodSelector";
+import MonthlyTrendsChart from "../components/reports/MonthlyTrendsChart";
+import MonthlyTrendsTable from "../components/reports/MonthlyTrendsTable";
+import CategoryOverTimeChart from "../components/reports/CategoryOverTimeChart";
+import CategoryOverTimeTable from "../components/reports/CategoryOverTimeTable";
+import ViewModeToggle, { readViewMode, type ViewMode } from "../components/reports/ViewModeToggle";
+import { useTrends } from "../hooks/useTrends";
+import { useReportsPeriod } from "../hooks/useReportsPeriod";
+import type { CategoryBreakdownItem } from "../shared/types";
+
+const STORAGE_KEY = "reports-viewmode-trends";
 
 export default function ReportsTrendsPage() {
   const { t } = useTranslation();
+  const { period, setPeriod, from, to, setCustomDates } = useReportsPeriod();
+  const { subView, setSubView, monthlyTrends, categoryOverTime, isLoading, error } = useTrends();
+  const [viewMode, setViewMode] = useState<ViewMode>(() => readViewMode(STORAGE_KEY));
+  const [hiddenCategories, setHiddenCategories] = useState<Set<string>>(new Set());
+
+  const preserveSearch = typeof window !== "undefined" ? window.location.search : "";
+
+  const toggleHidden = useCallback((name: string) => {
+    setHiddenCategories((prev) => {
+      const next = new Set(prev);
+      if (next.has(name)) next.delete(name);
+      else next.add(name);
+      return next;
+    });
+  }, []);
+
+  const showAll = useCallback(() => setHiddenCategories(new Set()), []);
+  // viewDetails not used in trends view — transactions details are accessed from category zoom.
+  const noOpDetails = useCallback((_item: CategoryBreakdownItem) => {}, []);
+
   return (
-    <div className="p-8 text-center text-[var(--muted-foreground)]">
+    <div className={isLoading ? "opacity-60" : ""}>
-      <h1 className="text-2xl font-bold mb-4">{t("reports.hub.trends")}</h1>
+      <div className="flex items-center gap-3 mb-4">
-      <p>{t("common.underConstruction")}</p>
+        <Link
+          to={`/reports${preserveSearch}`}
+          className="text-[var(--muted-foreground)] hover:text-[var(--foreground)] p-1 rounded-md hover:bg-[var(--muted)]"
+          aria-label={t("reports.hub.title")}
+        >
+          <ArrowLeft size={18} />
+        </Link>
+        <h1 className="text-2xl font-bold">{t("reports.hub.trends")}</h1>
+      </div>
+
+      <div className="flex flex-col sm:flex-row sm:items-center justify-between gap-4 mb-6 flex-wrap">
+        <PeriodSelector
+          value={period}
+          onChange={setPeriod}
+          customDateFrom={from}
+          customDateTo={to}
+          onCustomDateChange={setCustomDates}
+        />
+        <div className="flex gap-2 items-center flex-wrap">
+          <div className="inline-flex gap-1">
+            <button
+              type="button"
+              onClick={() => setSubView("global")}
+              aria-pressed={subView === "global"}
+              className={`px-3 py-2 rounded-lg text-sm font-medium transition-colors ${
+                subView === "global"
+                  ? "bg-[var(--primary)] text-white"
+                  : "bg-[var(--card)] border border-[var(--border)] text-[var(--foreground)] hover:bg-[var(--muted)]"
+              }`}
+            >
+              {t("reports.trends.subviewGlobal")}
+            </button>
+            <button
+              type="button"
+              onClick={() => setSubView("byCategory")}
+              aria-pressed={subView === "byCategory"}
+              className={`px-3 py-2 rounded-lg text-sm font-medium transition-colors ${
+                subView === "byCategory"
+                  ? "bg-[var(--primary)] text-white"
+                  : "bg-[var(--card)] border border-[var(--border)] text-[var(--foreground)] hover:bg-[var(--muted)]"
+              }`}
+            >
+              {t("reports.trends.subviewByCategory")}
+            </button>
+          </div>
+          <ViewModeToggle value={viewMode} onChange={setViewMode} storageKey={STORAGE_KEY} />
+        </div>
+      </div>
+
+      {error && (
+        <div className="bg-[var(--negative)]/10 text-[var(--negative)] rounded-xl p-4 mb-6">
+          {error}
+        </div>
+      )}
+
+      {subView === "global" ? (
+        viewMode === "chart" ? (
+          <MonthlyTrendsChart data={monthlyTrends} />
+        ) : (
+          <MonthlyTrendsTable data={monthlyTrends} />
+        )
+      ) : viewMode === "chart" ? (
+        <CategoryOverTimeChart
+          data={categoryOverTime}
+          hiddenCategories={hiddenCategories}
+          onToggleHidden={toggleHidden}
+          onShowAll={showAll}
+          onViewDetails={noOpDetails}
+        />
+      ) : (
+        <CategoryOverTimeTable data={categoryOverTime} hiddenCategories={hiddenCategories} />
+      )}
     </div>
   );
 }