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/hash.test.ts

@@ -0,0 +1,18 @@
+// tests/unit/scripts/i18n/hash.test.ts
+import { describe, expect, it } from "vitest";
+import { hash } from "../../../../scripts/i18n/lib/hash.mjs";
+
+describe("hash", () => {
+  it("is stable and 12 hex chars", () => {
+    expect(hash("hello world")).toMatch(/^[0-9a-f]{12}$/);
+    expect(hash("hello world")).toBe(hash("hello world"));
+  });
+
+  it("changes when source changes", () => {
+    expect(hash("a")).not.toBe(hash("b"));
+  });
+
+  it("normalizes CRLF to LF so line-ending churn does not re-translate", () => {
+    expect(hash("line1\r\nline2")).toBe(hash("line1\nline2"));
+  });
+});