feat: add GET /api/documents/latest returning latest version file with stamped ticket

Server-to-server endpoint for the e-Court backend (x-api-key against
DOCVER_API_KEY or EXTERNAL_API_KEY):
- type=pdf returns the latest version's PDF bytes (404 when absent)
- type=docx stamps fresh ticket custom properties (exp + HmacSha256 via
  addinTicketSecret(), Ed25519 when PRIVATE_KEY_HEX is set) into an
  in-memory copy before returning — MinIO object is never modified
- docId comes from fid inside the ticket_data query param, which must
  include fid/uid/uname so the stamped file stays redeemable by the
  add-in at /api/documents/token (buildStampedTicketData drops null
  values because parseDocverTicket rejects tid:null)
- adds parseTicketDataParam, parseLatestTypeParam, requireDocumentApiKey,
  findLatestVersionForDoc, getVersionObjectBytes + unit tests (320 pass)
- syncs PLAN-DOCVER.md, OpenAPI spec and .env.example

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

tests/lib/docver-token.test.ts

@@ -4,6 +4,7 @@ import { afterEach, describe, expect, it } from "vitest";
 import {
   issueDocverToken,
   parseTokenRequestBody,
+  requireDocumentApiKey,
   requireDocverApiKey,
   requireDocverBearer,
   verifyDocverToken,
@@ -30,12 +31,16 @@ function ok<T>(result: { ok: boolean } & T): asserts result is { ok: true } & T
 // --- env save/restore — require* อ่าน env ตอนเรียก ไม่ใช่ตอน module load
 const HAD_API_KEY = Object.prototype.hasOwnProperty.call(process.env, "DOCVER_API_KEY");
 const ORIG_API_KEY = process.env.DOCVER_API_KEY;
+const HAD_EXTERNAL_KEY = Object.prototype.hasOwnProperty.call(process.env, "EXTERNAL_API_KEY");
+const ORIG_EXTERNAL_KEY = process.env.EXTERNAL_API_KEY;
 const HAD_SECRET = Object.prototype.hasOwnProperty.call(process.env, "DOCVER_TOKEN_SECRET");
 const ORIG_SECRET = process.env.DOCVER_TOKEN_SECRET;
 
 afterEach(() => {
   if (HAD_API_KEY) process.env.DOCVER_API_KEY = ORIG_API_KEY;
   else delete process.env.DOCVER_API_KEY;
+  if (HAD_EXTERNAL_KEY) process.env.EXTERNAL_API_KEY = ORIG_EXTERNAL_KEY;
+  else delete process.env.EXTERNAL_API_KEY;
   if (HAD_SECRET) process.env.DOCVER_TOKEN_SECRET = ORIG_SECRET;
   else delete process.env.DOCVER_TOKEN_SECRET;
 });
@@ -175,6 +180,59 @@ describe("requireDocverApiKey", () => {
   });
 });
 
+// requireDocumentApiKey — auth ของ GET /api/documents/latest: x-api-key เทียบ
+// DOCVER_API_KEY หรือ EXTERNAL_API_KEY ตัวใดตัวหนึ่ง (ต่างจาก /token)
+describe("requireDocumentApiKey", () => {
+  function setKeys(docver: string | undefined, external: string | undefined): void {
+    if (docver === undefined) delete process.env.DOCVER_API_KEY;
+    else process.env.DOCVER_API_KEY = docver;
+    if (external === undefined) delete process.env.EXTERNAL_API_KEY;
+    else process.env.EXTERNAL_API_KEY = external;
+  }
+
+  it("ทั้งคู่ไม่ตั้ง / ว่าง / ช่องว่างล้วน = 401 fail closed ทุกกรณี", async () => {
+    for (const [docver, external] of [
+      [undefined, undefined],
+      ["", ""],
+      ["   ", "   "],
+    ] as const) {
+      setKeys(docver, external);
+      const res = requireDocumentApiKey(reqWithKey("test-key"));
+      expect(res?.status, `${docver}/${external}`).toBe(401);
+      expect(await bodyOf(res!)).toEqual({ error: "ระบบยังไม่ได้ตั้งค่า API key" });
+    }
+  });
+
+  it("ตั้งอันเดียวตัวไหนก็ผ่านเมื่อ key ตรงตัวนั้น · ตั้งทั้งคู่ตรงอันที่สองก็ผ่าน", () => {
+    setKeys("docver-key", undefined);
+    expect(requireDocumentApiKey(reqWithKey("docver-key"))).toBeNull();
+    expect(requireDocumentApiKey(reqWithKey("external-key"))?.status).toBe(401);
+
+    setKeys(undefined, "external-key");
+    expect(requireDocumentApiKey(reqWithKey("external-key"))).toBeNull();
+    expect(requireDocumentApiKey(reqWithKey("docver-key"))?.status).toBe(401);
+
+    setKeys("docver-key", "external-key");
+    expect(requireDocumentApiKey(reqWithKey("external-key"))).toBeNull();
+  });
+
+  it("ไม่ใส่ header กับ key ผิด ต้องได้ 401 ข้อความเดียวกันเป๊ะ (กัน enumerate)", async () => {
+    setKeys("docver-key", "external-key");
+    const missing = requireDocumentApiKey(reqWithKey());
+    const wrong = requireDocumentApiKey(reqWithKey("not-any-key"));
+    expect(missing?.status).toBe(401);
+    expect(wrong?.status).toBe(401);
+    expect(await bodyOf(missing!)).toEqual(await bodyOf(wrong!));
+  });
+
+  it("env มี whitespace รอบ ๆ ก็ trim ให้เทียบได้ทั้งสองตัว", () => {
+    setKeys("  docver-key  ", undefined);
+    expect(requireDocumentApiKey(reqWithKey("docver-key"))).toBeNull();
+    setKeys(undefined, "  external-key  ");
+    expect(requireDocumentApiKey(reqWithKey("external-key"))).toBeNull();
+  });
+});
+
 describe("requireDocverBearer", () => {
   it("ทุกกรณีพ้นสภาพ (ไม่มี header / ไม่ใช่ Bearer / token เน่า / หมดอายุ / secret ไม่ตั้ง) = 401 ข้อความเดียวกัน", async () => {
     const deniedBodies = new Set<string>();