feat: add auto-increment id, size/duration tracking, and soft cleanup to conversion_jobs

Rename the old CHAR(36) id to uuid (still used for public URLs and file
naming) and add a real auto-increment id as the primary key. Track
input/output file size and conversion duration per job. Cleanup no
longer deletes rows; it marks cleaned_at and skips already-cleaned
expired jobs on later runs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/worker.js

@@ -1,4 +1,5 @@
 import { pathToFileURL } from 'node:url';
+import fs from 'node:fs/promises';
 import { loadConfig } from './config.js';
 import { getPool } from './db.js';
 import { ensureStorageDirs, uploadPath, outputPath, deleteIfExists } from './storage.js';
@@ -22,8 +23,8 @@ function withTimeout(promise, ms) {
 async function processJob(pool, config, job) {
   await markProcessing(pool, job.id);
 
-  const inputFilePath = uploadPath(config, job.id, job.sourceFormat);
-  const outputFilePath = outputPath(config, job.id, job.targetFormat);
+  const inputFilePath = uploadPath(config, job.uuid, job.sourceFormat);
+  const outputFilePath = outputPath(config, job.uuid, job.targetFormat);
 
   try {
     const entry = resolveConverter(job.sourceFormat, job.targetFormat);
@@ -31,11 +32,16 @@ async function processJob(pool, config, job) {
       throw new Error(`No converter registered for ${job.sourceFormat} -> ${job.targetFormat}`);
     }
 
+    const startedAt = Date.now();
     await withTimeout(entry.convert(inputFilePath, outputFilePath), JOB_TIMEOUT_MS);
+    const conversionDurationSeconds = (Date.now() - startedAt) / 1000;
+    const { size: outputSizeBytes } = await fs.stat(outputFilePath);
 
     await markDone(pool, job.id, {
-      outputPath: `${job.id}.${job.targetFormat}`,
+      outputPath: `${job.uuid}.${job.targetFormat}`,
       outputMimeType: outputMimeType(job.targetFormat),
+      outputSizeBytes,
+      conversionDurationSeconds,
     });
   } catch (error) {
     await deleteIfExists(outputFilePath);