YT Music-koppling i settings: Googles device-flöde inbyggt

- POST /api/ytmusic/start + /poll: kör device-flödet mot Google och
  skriver ytmusicapi-kompatibel oauth.json till Youtubarrs datamapp
  (mounten byts till rw i stacken)
- Settings-sektion: Client ID/secret, 'Spara & koppla' visar kod + länk
  och pollar tills godkänt; 'Testa kopplingen' verifierar med en
  token-förnyelse mot Google
- 4 nya tester, totalt 21

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01824ZrvG2mDYYrmwqypLNup

backend/test/ytmusic.test.js

@@ -0,0 +1,89 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { existsSync, mkdtempSync, readFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import path from 'node:path'
+import { settingsStore } from '../src/settings.js'
+import { ytmusicFlow } from '../src/ytmusic.js'
+
+function setup() {
+  const dataDir = mkdtempSync(path.join(tmpdir(), 'lyssnarr-yt-'))
+  const store = settingsStore(dataDir)
+  store.save({ ytmusic: { clientId: 'klient-id', clientSecret: 'klient-hemlis' } })
+  const config = { youtubarr: { dataDir } }
+  return { dataDir, store, config }
+}
+
+test('start returnerar kod och länk från Google', async () => {
+  const { store, config } = setup()
+  const flow = ytmusicFlow({
+    config,
+    store,
+    fetchImpl: async (url, opts) => {
+      assert.match(url, /device\/code/)
+      assert.match(opts.body, /client_id=klient-id/)
+      return {
+        ok: true,
+        json: async () => ({
+          device_code: 'dev-123',
+          user_code: 'ABCD-EFGH',
+          verification_url: 'https://www.google.com/device',
+          interval: 5,
+          expires_in: 1800,
+        }),
+      }
+    },
+  })
+  const out = await flow.start()
+  assert.equal(out.userCode, 'ABCD-EFGH')
+  assert.equal(out.deviceCode, 'dev-123')
+})
+
+test('start utan client id ger fel', async () => {
+  const dataDir = mkdtempSync(path.join(tmpdir(), 'lyssnarr-yt-'))
+  const flow = ytmusicFlow({ config: { youtubarr: { dataDir } }, store: settingsStore(dataDir) })
+  const out = await flow.start()
+  assert.match(out.error, /Client ID/i)
+})
+
+test('poll: pending -> klar skriver ytmusicapi-kompatibel oauth.json', async () => {
+  const { dataDir, store, config } = setup()
+  let calls = 0
+  const flow = ytmusicFlow({
+    config,
+    store,
+    fetchImpl: async () => {
+      calls++
+      if (calls === 1) return { ok: false, json: async () => ({ error: 'authorization_pending' }) }
+      return {
+        ok: true,
+        json: async () => ({
+          access_token: 'acc',
+          refresh_token: 'ref',
+          expires_in: 3600,
+          scope: 'https://www.googleapis.com/auth/youtube',
+          token_type: 'Bearer',
+        }),
+      }
+    },
+  })
+  assert.deepEqual(await flow.poll('dev-123'), { status: 'pending' })
+  assert.deepEqual(await flow.poll('dev-123'), { status: 'klar' })
+  const p = path.join(dataDir, 'oauth.json')
+  assert.ok(existsSync(p))
+  const tok = JSON.parse(readFileSync(p, 'utf8'))
+  assert.equal(tok.access_token, 'acc')
+  assert.equal(tok.refresh_token, 'ref')
+  assert.equal(tok.token_type, 'Bearer')
+  assert.ok(tok.expires_at > Math.floor(Date.now() / 1000))
+})
+
+test('poll: avslag ger felstatus', async () => {
+  const { store, config } = setup()
+  const flow = ytmusicFlow({
+    config,
+    store,
+    fetchImpl: async () => ({ ok: false, json: async () => ({ error: 'access_denied', error_description: 'nekad' }) }),
+  })
+  assert.deepEqual(await flow.poll('dev-123'), { status: 'error', message: 'nekad' })
+})