Merge PR #1038: surface add-time failures as failed done entries

Adds __record_add_failure so a URL that fails before a real download starts
(unsupported/unextractable URL, SSRF-rejected, extraction error) appears in the
Completed list as a red-cross entry with retry and error-detail, instead of only
a transient toast and a server log line. Keyed by info.url like any errored
download. Includes _short_title_for_failed_url for a readable hostname title.

The frontend hunk removing the 'Click for details' hint from every error row was
dropped from this merge; that affordance (added in fd3aaea, #143) is kept.

Co-authored-by: streamer1122 <streamer1122@users.noreply.github.com>

app/tests/test_download_queue.py

@@ -115,6 +115,54 @@ async def test_add_single_video_goes_to_pending_when_auto_start_false(dq_env):
     assert dq.pending.exists("https://example.com/watch?v=1")
 
 
+@pytest.mark.asyncio
+async def test_add_unsupported_url_recorded_as_failed_entry(dq_env):
+    """An unsupported/unextractable URL must show up as a red-cross entry in the
+    done list, not just a transient toast and a server log line."""
+    import ytdl
+
+    notifier = AsyncMock()
+    url = "https://example.com/not-a-video"
+
+    def boom(self, url, ytdl_options_presets=None, ytdl_options_overrides=None):
+        raise ytdl.yt_dlp.utils.YoutubeDLError(f'Unsupported URL: {url}')
+
+    dq = DownloadQueue(dq_env, notifier)
+    with patch.object(DownloadQueue, "_DownloadQueue__extract_info", boom):
+        result = await dq.add(
+            url, "video", "auto", "any", "best", "", "", 0, auto_start=True,
+        )
+    assert result["status"] == "error"
+    assert dq.done.exists(url)
+    failed = dq.done.get(url)
+    assert failed.info.status == "error"
+    assert failed.info.error == result["msg"]
+    assert failed.info.url == url
+    # The full URL stays in .url/.error for the detail panel; the display
+    # title is shortened to the hostname so the Completed row stays readable.
+    assert failed.info.title == "example.com"
+    notifier.completed.assert_awaited()
+
+
+@pytest.mark.asyncio
+async def test_add_ssrf_rejected_url_recorded_as_failed_entry(dq_env):
+    """A URL rejected by the SSRF guard (before yt-dlp ever runs) must also
+    surface as a failed entry, not just an error status returned to the caller."""
+    notifier = AsyncMock()
+    url = "file:///etc/passwd"
+
+    dq = DownloadQueue(dq_env, notifier)
+    result = await dq.add(
+        url, "video", "auto", "any", "best", "", "", 0, auto_start=True,
+    )
+    assert result["status"] == "error"
+    assert dq.done.exists(url)
+    failed = dq.done.get(url)
+    assert failed.info.status == "error"
+    assert failed.info.error == result["msg"]
+    notifier.completed.assert_awaited()
+
+
 @pytest.mark.asyncio
 async def test_cancel_removes_from_pending(dq_env):
     notifier = AsyncMock()