fix(scheduler,i18n): a failure a job names reads in the reader's language

The audit log showed a failed RSS poll as the server's English sentence
under a Hungarian UI. A job can now raise progress.JobFailed(reason,
message, **params): the scheduler stores the reason and params as the
run's data (dashboard, manual-run notice, audit row) beside the English
line, and the client renders scheduler.failure.<reason>. The RSS outage
names its first channel and the reason code (HTTP 404 vs unreachable).
An upstream's own error text stays as raised (diagnostic).

backend/tests/test_sync_guards.py

@@ -6,6 +6,7 @@ import logging
 import httpx
 import pytest
 
+from app import progress
 from app.sync import runner
 from app.sync.playlists import FAILED, _Breaker
 from app.sync.subscriptions import should_prune
@@ -224,8 +225,15 @@ class TestRssPollResult:
         def dead(cid):
             raise rss.RssError(f"RSS fetch for {cid} returned HTTP 404", "http_404")
 
-        with pytest.raises(RuntimeError, match="HTTP 404"):
+        with pytest.raises(RuntimeError, match="HTTP 404") as err:
             self._run(monkeypatch, fetch=dead, apply_=lambda db, ch, e: 1, channels=("UC_dead",))
+        # E31: and as data, for the reader's language — whose feed, and the reason code that tells a
+        # dead feed (`http_404`) from a dead egress (`transport`).
+        assert isinstance(err.value, progress.JobFailed)
+        assert (err.value.reason, err.value.params) == (
+            "rss_all_failed",
+            {"total": 1, "channel": "UC_dead", "cause": "http_404", "read": 0},
+        )
 
     def test_a_read_only_database_is_a_total_outage_too(self, monkeypatch):
         # Every feed reads fine, nothing can be stored: just as un-polled, just as red.