feat: add usage statistics page, CLI improvements, and UI enhancements

- Add Usage Stats page with token breakdown, model distribution, and 30-day trend
- Pass through cache/cost token fields in BFF (cache_read/write_tokens, reasoning_tokens, actual_cost_usd)
- Add CLI commands: -v/--version, -h/--help, update/upgrade with auto-restart
- Auto-open browser on startup, auto-kill port conflicts (cross-platform)
- Validate all api_server config fields on startup (enabled, host, port, key, cors_origins)
- Add streaming thinking video animation with tool calls panel
- Add context token usage display (used / total) in chat header
- Sidebar: white logo area with shadow, dance video beside logo (canvas seamless loop)
- Fix sidebar nav scroll (app-main overflow-y: auto)

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

src/views/UsageView.vue

@@ -0,0 +1,73 @@
+<script setup lang="ts">
+import { NButton } from 'naive-ui'
+import { onMounted } from 'vue'
+import { useI18n } from 'vue-i18n'
+import { useUsageStore } from '@/stores/usage'
+import StatCards from '@/components/usage/StatCards.vue'
+import ModelBreakdown from '@/components/usage/ModelBreakdown.vue'
+import DailyTrend from '@/components/usage/DailyTrend.vue'
+
+const { t } = useI18n()
+const usageStore = useUsageStore()
+
+onMounted(() => {
+  usageStore.loadSessions()
+})
+</script>
+
+<template>
+  <div class="usage-view">
+    <header class="usage-header">
+      <h2 class="usage-title">{{ t('usage.title') }}</h2>
+      <NButton size="small" quaternary :loading="usageStore.isLoading" @click="usageStore.loadSessions()">
+        {{ t('usage.refresh') }}
+      </NButton>
+    </header>
+
+    <div v-if="usageStore.isLoading && usageStore.sessions.length === 0" class="usage-loading">
+      {{ t('common.loading') }}
+    </div>
+
+    <template v-else-if="usageStore.sessions.length > 0">
+      <StatCards />
+      <ModelBreakdown />
+      <DailyTrend />
+    </template>
+
+    <div v-else class="usage-empty">
+      {{ t('usage.noData') }}
+    </div>
+  </div>
+</template>
+
+<style scoped lang="scss">
+@use '@/styles/variables' as *;
+
+.usage-view {
+  padding: 24px;
+  max-width: 960px;
+  margin: 0 auto;
+}
+
+.usage-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 20px;
+}
+
+.usage-title {
+  font-size: 18px;
+  font-weight: 600;
+  color: $text-primary;
+  margin: 0;
+}
+
+.usage-loading,
+.usage-empty {
+  text-align: center;
+  padding: 60px 0;
+  color: $text-muted;
+  font-size: 14px;
+}
+</style>