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).

frontend/src/lib/jobResult.dom.test.ts

@@ -4,7 +4,7 @@
 // one-liner was "recent={'channels_processed': 0, …}, deep={…}" — English keys and a Python repr.
 import { afterEach, describe, expect, it } from "vitest";
 import i18n, { setLanguage } from "../i18n";
-import { jobResultText, parseSummary } from "./jobResult";
+import { jobFailureText, jobResultText, jobRunText, parseSummary } from "./jobResult";
 
 afterEach(() => setLanguage("en"));
 
@@ -65,3 +65,34 @@ describe("an older notice's one-liner", () => {
     expect(parseSummary(null)).toBeNull();
   });
 });
+
+// E31: the audit log showed a failed RSS poll as the server's English sentence ("RSS poll failed for
+// all 399 channels — first: …") under a Hungarian UI. A failure the job names rides along as data.
+describe("a failed run", () => {
+  const run = {
+    job_id: "rss_poll",
+    status: "error",
+    summary:
+      "RSS poll failed for all 399 channels — first: UCx: RSS fetch for UCx returned HTTP 404",
+    result: { failure: "rss_all_failed", total: 1399, channel: "UCx", cause: "http_404", read: 0 },
+  };
+
+  it("says the failure the job named in the reader's language", () => {
+    const t = i18n.getFixedT("hu");
+    expect(jobRunText(t, run, "hu").body).toBe(
+      "Az RSS-hírcsatorna egyik csatornánál sem válaszolt (1399) — az első: UCx, HTTP 404. " +
+        "Az API-n át beolvasva helyette: 0",
+    );
+    expect(jobFailureText(t, { ...run.result, cause: "transport" }, "hu")).toContain(
+      "UCx, nem érhető el.",
+    );
+  });
+
+  it("keeps any other failure's own text", () => {
+    const t = i18n.getFixedT("hu");
+    expect(jobRunText(t, { ...run, summary: "Plex returned 500", result: null }, "hu").body).toBe(
+      "Plex returned 500",
+    );
+    expect(jobFailureText(t, { failure: "moon_is_full" }, "hu")).toBeNull();
+  });
+});