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/routes/api/jobs/[id]/retry/+server.ts

@@ -8,9 +8,6 @@ export async function POST({ params }) {
 	if (!['failed', 'cancelled'].includes(job.status)) {
 		throw error(409, 'Only failed or cancelled jobs can be retried');
 	}
-	if (!job.source.startsWith('http')) {
-		throw error(422, 'Cannot retry a file upload — please re-upload the file');
-	}
 	await retryJob(params.id);
 	return json({ ok: true });
 }

src/routes/api/webhook/[jobId]/+server.ts

@@ -2,7 +2,7 @@ import { json, error } from '@sveltejs/kit';
 import { getJob, updateJob, setJobStatus } from '$lib/server/db.js';
 import { writeOutputs } from '$lib/server/formatter.js';
 import { sendNotification } from '$lib/server/push.js';
-import { cleanupJobTmp } from '$lib/server/downloader.js';
+import { cleanupJobTmp, cleanupUploadDir } from '$lib/server/downloader.js';
 import { emitProgress } from '$lib/server/pipeline.js';
 import type { Segment, WhisperJob } from '$lib/types.js';
 
@@ -79,6 +79,7 @@ export async function POST({ params, request }) {
 
 		await sendNotification(jobId, '✅ Transcript ready', job.title);
 		await cleanupJobTmp(jobId);
+		await cleanupUploadDir(jobId).catch(() => {});
 
 		return json({ ok: true });
 	} catch (err: unknown) {