feat(panel): in-panel API documentation page

New /panel/api-docs route with a one-page reference covering every
/panel/api/* endpoint (Auth, Inbounds, Server, Nodes, Custom Geo,
Backup) plus a Bearer-token primer that reads the current token and
exposes Show/Copy/Regenerate inline. Sidebar gets an API Docs entry
right after Xray; the menu label is shared via menu.apiDocs across all
13 locales.

frontend/src/pages/api-docs/EndpointSection.vue

@@ -0,0 +1,65 @@
+<script setup>
+import EndpointRow from './EndpointRow.vue';
+
+defineProps({
+  section: { type: Object, required: true },
+});
+</script>
+
+<template>
+  <section :id="section.id" class="api-section">
+    <h2 class="section-title">{{ section.title }}</h2>
+    <p v-if="section.description" class="section-description">{{ section.description }}</p>
+    <div class="endpoints">
+      <EndpointRow v-for="(endpoint, idx) in section.endpoints" :key="idx" :endpoint="endpoint" />
+    </div>
+  </section>
+</template>
+
+<style scoped>
+.api-section {
+  background: #fff;
+  border: 1px solid rgba(128, 128, 128, 0.15);
+  border-radius: 8px;
+  padding: 20px 24px;
+  margin-bottom: 20px;
+  scroll-margin-top: 16px;
+}
+
+.section-title {
+  font-size: 20px;
+  font-weight: 600;
+  margin: 0;
+  color: rgba(0, 0, 0, 0.88);
+}
+
+.section-description {
+  margin: 6px 0 14px;
+  color: rgba(0, 0, 0, 0.65);
+  line-height: 1.55;
+}
+
+.endpoints > :first-child {
+  padding-top: 0;
+}
+</style>
+
+<style>
+body.dark .api-section {
+  background: #252526;
+  border-color: rgba(255, 255, 255, 0.1);
+}
+
+html[data-theme='ultra-dark'] .api-section {
+  background: #0a0a0a;
+  border-color: rgba(255, 255, 255, 0.08);
+}
+
+body.dark .section-title {
+  color: rgba(255, 255, 255, 0.92);
+}
+
+body.dark .section-description {
+  color: rgba(255, 255, 255, 0.7);
+}
+</style>