feat(i18n): 21-language pipeline, landing/docs/API wiring, landing+API translations

Shared Claude Code translation pipeline (scripts/i18n, no API key) plus Astro/VitePress/Scalar i18n wiring. Landing and API reference translated into all 20 languages; docs i18n wiring + English source anchors. The translated docs markdown (apps/docs/<locale>/**, 3,620 files) follows in a companion PR because it exceeds GitHub's per-PR CI file limit.

apps/docs/.vitepress/theme/FundButton.vue

@@ -1,14 +1,24 @@
+<script setup lang="ts">
+import { useData } from "vitepress";
+import { computed } from "vue";
+import { normalizeLocale, t } from "../i18n/ui.mjs";
+
+const { lang } = useData();
+const locale = computed(() => normalizeLocale(lang.value));
+const label = computed(() => t(locale.value, "fund.label"));
+</script>
+
 <template>
   <a
     href="https://github.com/sponsors/snapotter-hq"
     target="_blank"
     rel="noopener"
     class="fund-btn"
-    title="Fund Development"
+    :title="label"
   >
     <svg class="fund-icon" width="14" height="14" viewBox="0 0 24 24" fill="currentColor">
       <path d="M12 21.35l-1.45-1.32C5.4 15.36 2 12.28 2 8.5 2 5.42 4.42 3 7.5 3c1.74 0 3.41.81 4.5 2.09C13.09 3.81 14.76 3 16.5 3 19.58 3 22 5.42 22 8.5c0 3.78-3.4 6.86-8.55 11.54L12 21.35z"/>
     </svg>
-    <span>Fund Development</span>
+    <span>{{ label }}</span>
   </a>
 </template>