feat: 账单支出图表（按平台月度支出柱状图）

static/js/app.js

@@ -332,6 +332,10 @@ const SubscriptionsView = {
         <div class="text-xs text-slate-400 mt-1">年度约 {{ (v*12).toFixed(2) }}</div>
       </div>
     </div>
+    <div v-if="subs.length" class="bg-white dark:bg-slate-900 rounded-xl border border-slate-200 dark:border-slate-800 p-4">
+      <h3 class="font-semibold mb-2 text-sm">按平台月度支出（换算为月均）</h3>
+      <canvas id="billingChart" height="80"></canvas>
+    </div>
     <div class="bg-white dark:bg-slate-900 rounded-xl border border-slate-200 dark:border-slate-800 overflow-hidden">
       <table class="w-full text-sm">
         <thead class="bg-slate-50 dark:bg-slate-800/50 text-slate-500 text-left text-xs">
@@ -372,7 +376,37 @@ const SubscriptionsView = {
       }
       return m;
     });
-    return { store, Fmt, subs, monthlyByCurrency };
+    const byProviderMonthly = computed(() => {
+      const m = {};
+      for (const a of subs.value) {
+        const prov = a.provider_name || a.provider;
+        m[prov] = (m[prov] || 0) + normalizedMonthly(a.cost, a.renewal_cycle);
+      }
+      return m;
+    });
+    let billingChart = null;
+    function renderBillingChart() {
+      const canvas = document.getElementById('billingChart');
+      if (!canvas || !window.Chart) return;
+      const entries = Object.entries(byProviderMonthly.value).sort((x, y) => y[1] - x[1]);
+      if (!entries.length) return;
+      if (billingChart) { billingChart.destroy(); billingChart = null; }
+      billingChart = new Chart(canvas, {
+        type: 'bar',
+        data: {
+          labels: entries.map(e => e[0]),
+          datasets: [{ label: '月度支出', data: entries.map(e => e[1].toFixed(2)), backgroundColor: '#6366f1', borderRadius: 6 }],
+        },
+        options: {
+          responsive: true,
+          scales: { y: { beginAtZero: true } },
+          plugins: { legend: { display: false } },
+        },
+      });
+    }
+    watch([subs, byProviderMonthly], () => { nextTick(renderBillingChart); }, { deep: true });
+    onMounted(() => { nextTick(renderBillingChart); });
+    return { store, Fmt, subs, monthlyByCurrency, byProviderMonthly };
   },
 };