D2: Widen retry to upload-source jobs

- Remove http-only guard in retry endpoint (src/routes/api/jobs/[id]/retry/+server.ts)
- Extend pipeline.ts retryJob() to handle upload-source jobs:
  read file from persistent storage, pass buffer to runJob
- Change saveUploadedFile() to save to DATA_DIR/uploads/{jobId}/
  (survives cleanupJobTmp, available for retry on failure)
- Add getUploadPath(), cleanupUploadDir() to downloader.ts
- Remove cleanupFiles(rawAudioPath) from catch block in runJob()
  — cleanupJobTmp handles TMP_DIR for YouTube, uploads survive
- Add cleanupUploadDir() on webhook success path
- Add retry-endpoint.test.ts with 9 tests covering:
  - 404 for unknown job
  - 409 for non-retryable status (done, pending)
  - 200 for cancelled (retryable)
  - 200 for failed YouTube job (existing behavior)
  - 200 for failed upload-source job (new behavior, .webm and .mp3)
  - Negative: retryJob not called on 404/409
- Add downloader.test.ts tests for saveUploadedFile persistent path,
  getUploadPath, cleanupUploadDir, isolation, and non-existent cleanup
- Fix webhook.test.ts mock to include cleanupUploadDir

All 189 tests pass across 12 test files.

src/lib/server/downloader.ts

@@ -6,12 +6,34 @@ import { join } from 'path';
 import { fetchTranscript, type TranscriptResponse } from 'youtube-transcript';
 
 const execFileAsync = promisify(execFile);
-const TMP_DIR = join(process.env.DATA_DIR ?? '/tmp/.whisper-pwa', 'downloads');
+const DATA_DIR = process.env.DATA_DIR ?? '/tmp/.whisper-pwa';
+const TMP_DIR = join(DATA_DIR, 'downloads');
+const UPLOADS_DIR = join(DATA_DIR, 'uploads');
 
 export async function ensureTmpDir() {
 	if (!existsSync(TMP_DIR)) await mkdir(TMP_DIR, { recursive: true });
 }
 
+async function ensureUploadsDir(jobId: string): Promise<string> {
+	const dir = join(UPLOADS_DIR, jobId);
+	if (!existsSync(dir)) await mkdir(dir, { recursive: true });
+	return dir;
+}
+
+/** Path to a job's persistent upload file. Survives cleanupJobTmp. */
+export function getUploadPath(jobId: string, filename: string): string {
+	return join(UPLOADS_DIR, jobId, filename);
+}
+
+/** Delete a job's persistent upload dir (call on success). */
+export async function cleanupUploadDir(jobId: string): Promise<void> {
+	const dir = join(UPLOADS_DIR, jobId);
+	try {
+		const { rm } = await import('fs/promises');
+		await rm(dir, { recursive: true, force: true });
+	} catch { /* ignore */ }
+}
+
 export interface CaptionResult {
 	type: 'captions';
 	segments: Array<{ index: number; start: number; end: number; text: string; words: [] }>;
@@ -93,15 +115,13 @@ export async function downloadYouTube(url: string, jobId: string): Promise<Downl
 	return { type: 'audio', audioPath, title };
 }
 
-/** Save an uploaded file to tmp dir and return its path. */
+/** Save an uploaded file to persistent storage (survives cleanupJobTmp). */
 export async function saveUploadedFile(
 	buffer: Buffer,
 	filename: string,
 	jobId: string
 ): Promise<string> {
-	await ensureTmpDir();
-	const outDir = join(TMP_DIR, jobId);
-	await mkdir(outDir, { recursive: true });
+	const outDir = await ensureUploadsDir(jobId);
 	const dest = join(outDir, filename);
 	await writeFile(dest, buffer);
 	return dest;