Survive a first full crawl: poll, time out on silence, retry downloads

The first full crawl with the file manager ran 14 minutes, downloading every
file once, and broke in three ways:

- `schulcloud refresh` reported "fetch failed" for a crawl that was
  succeeding: Node's fetch abandons a response without headers after five
  minutes. POST /api/refresh takes wait:false and the CLI polls /api/status;
  refresh_index answers after 50 s and leaves the crawl running, and
  index_status says when a first crawl is under way.
- Downloads were bounded by the 30 s request timeout, which cut 11 MB scans
  off mid-transfer. They now time out on 30 s of silence instead.
- Failures were recorded once and never retried. A download failure is now
  retried on the next crawl while an extraction failure stays final, and PDF
  text containing NUL, which Postgres refuses, is stripped.

On the re-crawl all six failed files succeeded; only two videos above the
mirror cap stay metadata-only, by design. 137 tests.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/bin/cli.ts

@@ -236,7 +236,14 @@ async function refresh(flags: Flags): Promise<number> {
 	const api = new ApiClient(await loadCliConfig());
 	const scope = flags.course ? String(flags.course) : undefined;
 	process.stderr.write(`Asking the server to re-crawl ${scope ? `course ${scope}` : 'everything'}…\n`);
-	const result = (await api.refresh(scope, Boolean(flags.force))) as {
+	let lastNote = 0;
+	const result = (await api.refresh(scope, Boolean(flags.force), (seconds) => {
+		// A note every half minute, so a long first crawl does not look hung.
+		if (seconds - lastNote >= 30) {
+			lastNote = seconds;
+			process.stderr.write(`  still crawling… ${seconds}s\n`);
+		}
+	})) as {
 		crawlId: number; courses: number; files: number; mirrored: number; extracted: number;
 		skipped: number; durationMs: number; joined?: boolean;
 	};