feat(TRUEREF-0022): complete iteration 0 — worker-thread indexing, parallel jobs, SSE progress

- Move IndexingPipeline.run() into Worker Threads via WorkerPool
- Add dedicated embedding worker thread with single model instance
- Add stage/stageDetail columns to indexing_jobs schema
- Create ProgressBroadcaster for SSE channel management
- Add SSE endpoints: GET /api/v1/jobs/:id/stream, GET /api/v1/jobs/stream
- Replace UI polling with EventSource on repo detail and admin pages
- Add concurrency settings UI and API endpoint
- Build worker entries separately via esbuild

scripts/build-workers.mjs

@@ -0,0 +1,38 @@
+import * as esbuild from 'esbuild';
+import { existsSync } from 'node:fs';
+
+const entries = [
+	'src/lib/server/pipeline/worker-entry.ts',
+	'src/lib/server/pipeline/embed-worker-entry.ts'
+];
+
+try {
+	const existing = entries.filter(e => existsSync(e));
+	if (existing.length === 0) {
+		console.log('[build-workers] No worker entry files found yet, skipping.');
+		process.exit(0);
+	}
+
+	await esbuild.build({
+		entryPoints: existing,
+		bundle: true,
+		platform: 'node',
+		target: 'node20',
+		format: 'esm',
+		outdir: 'build/workers',
+		outExtension: { '.js': '.mjs' },
+		alias: {
+			'$lib': './src/lib',
+			'$lib/server': './src/lib/server'
+		},
+		external: ['better-sqlite3', '@xenova/transformers'],
+		banner: {
+			js: "import { createRequire } from 'module'; const require = createRequire(import.meta.url);"
+		}
+	});
+
+	console.log(`[build-workers] Compiled ${existing.length} worker(s) to build/workers/`);
+} catch (err) {
+	console.error('[build-workers] Error:', err);
+	process.exit(1);
+}