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.

tests/unit/scripts/i18n/claude.test.ts

@@ -0,0 +1,21 @@
+// tests/unit/scripts/i18n/claude.test.ts
+import { describe, expect, it, vi } from "vitest";
+import { makeTranslator } from "../../../../scripts/i18n/lib/claude.mjs";
+
+describe("makeTranslator", () => {
+  it("masks input, sends one call per unit, restores tokens, returns id->text", async () => {
+    const send = vi.fn(async ({ text }) => `DE(${text})`);
+    const translate = makeTranslator({ send });
+    const units = [
+      { id: "a", sourceText: "Hello `code`", kind: "markdown" },
+      { id: "b", sourceText: "See {n} files", kind: "markdown" },
+    ];
+    const out = await translate(units, "de");
+    // Tokens were restored, so the code span and placeholder survive verbatim.
+    expect(out.get("a")).toContain("`code`");
+    expect(out.get("b")).toContain("{n}");
+    expect(send).toHaveBeenCalledTimes(2);
+    // The masked text sent to the model must NOT contain the raw code span.
+    expect(send.mock.calls[0][0].text).not.toContain("`code`");
+  });
+});