fix: Codex review P2 issues + frontend test failure

- Reset download_phase when transitioning to paused (pause(), update_status(),
  _post_download_cleanup()) so UI shows 'Paused' instead of stale phase label
- Reset download_phase when starting/resuming download (start() preparing state)
- Count 'postprocessing' as active download in updateMetrics() so dashboard
  shows accurate counts during ffmpeg post-processing
- Add missing completedDownload Subject to DownloadsServiceStub in app.spec.ts
- Add Download type import to app.spec.ts

Fixes: TypeError Cannot read properties of undefined (reading 'pipe')
       at app.ts:300 (completedDownload not in test stub)

app/ytdl.py

@@ -647,6 +647,7 @@ class Download:
         self.loop = asyncio.get_running_loop()
         self.notifier = notifier
         self.info.status = 'preparing'
+        self.info.download_phase = None
         await self.notifier.updated(self.info)
         self.status_task = asyncio.create_task(self.update_status())
         await self.loop.run_in_executor(None, self.proc.join)
@@ -673,6 +674,7 @@ class Download:
         self.paused = True
         self.start_generation += 1
         self.info.status = 'paused'
+        self.info.download_phase = None
         self.info.speed = None
         self.info.eta = None
         if self.running():
@@ -705,6 +707,7 @@ class Download:
                 return
             if self.paused:
                 self.info.status = 'paused'
+                self.info.download_phase = None
                 self.info.speed = None
                 self.info.eta = None
                 await self.notifier.updated(self.info)
@@ -988,6 +991,7 @@ class DownloadQueue:
         key = getattr(download.info, 'key', download.info.url)
         if download.paused:
             download.info.status = 'paused'
+            download.info.download_phase = None
             download.info.speed = None
             download.info.eta = None
             download.close()

ui/src/app/app.spec.ts

@@ -5,6 +5,7 @@ import { App } from './app';
 import { DownloadsService } from './services/downloads.service';
 import { SubscriptionsService } from './services/subscriptions.service';
 import { CookieService } from 'ngx-cookie-service';
+import { Download } from './interfaces';
 
 class DownloadsServiceStub {
   loading = false;
@@ -18,6 +19,7 @@ class DownloadsServiceStub {
   customDirsChanged = new Subject<Record<string, string[]>>();
   ytdlOptionsChanged = new Subject<Record<string, unknown>>();
   updated = new Subject<void>();
+  completedDownload = new Subject<Download>();
 
   getCookieStatus() {
     return of({ status: 'ok', has_cookies: false });

ui/src/app/app.ts

@@ -1651,6 +1651,8 @@ export class App implements AfterViewInit, OnInit, OnDestroy {
         speed += download.speed || 0;
       } else if (download.status === 'preparing') {
         active++;
+      } else if (download.status === 'postprocessing') {
+        active++;
       } else if (download.status === 'pending' || download.status === 'paused') {
         queued++;
       }