internaluploader: server + docs

One-way upload server: authentik SSO pairing (QR + app-initiated deep
link), hashed device tokens, streamed sha256-verified uploads into the
metube directory as <sha256>.<ext>.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/test/tokens.test.ts

@@ -0,0 +1,42 @@
+import assert from "node:assert/strict";
+import { mkdtempSync } from "node:fs";
+import { readFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { test } from "node:test";
+
+import { TokenStore } from "../src/tokens.ts";
+
+test("pairing code round-trip mints a working device token", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "tokens-"));
+  const store = new TokenStore(dir, 60_000);
+
+  const pairing = store.issuePairingCode("michal");
+  assert.match(pairing.code, /^[0-9a-f]{64}$/);
+
+  const redeemed = store.redeemPairingCode(pairing.code);
+  assert.ok(redeemed);
+  assert.equal(redeemed.username, "michal");
+
+  // Single use.
+  assert.equal(store.redeemPairingCode(pairing.code), undefined);
+
+  // The token authenticates, wrong tokens do not.
+  assert.equal(store.authenticate(redeemed.token), "michal");
+  assert.equal(store.authenticate("not-a-token"), undefined);
+
+  // Nothing on disk contains the plaintext token.
+  const persisted = await readFile(join(dir, "devices.json"), "utf8");
+  assert.ok(!persisted.includes(redeemed.token));
+
+  // A fresh store reads the same devices back.
+  const reloaded = new TokenStore(dir, 60_000);
+  assert.equal(reloaded.authenticate(redeemed.token), "michal");
+});
+
+test("expired pairing codes are refused", () => {
+  const dir = mkdtempSync(join(tmpdir(), "tokens-"));
+  const store = new TokenStore(dir, -1); // already expired at issue time
+  const pairing = store.issuePairingCode("michal");
+  assert.equal(store.redeemPairingCode(pairing.code), undefined);
+});