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

src/routes/api/v1/jobs/stream/+server.ts

@@ -0,0 +1,52 @@
+/**
+ * GET /api/v1/jobs/stream — stream real-time job progress for all jobs or a specific repository via SSE.
+ *
+ * Query parameters:
+ *   repositoryId (optional) — filter to jobs for this repository
+ */
+
+import type { RequestHandler } from './$types';
+import { getBroadcaster } from '$lib/server/pipeline/progress-broadcaster.js';
+import { handleServiceError } from '$lib/server/utils/validation.js';
+
+export const GET: RequestHandler = ({ url }) => {
+	try {
+		const broadcaster = getBroadcaster();
+		if (!broadcaster) {
+			return new Response('Service unavailable', { status: 503 });
+		}
+
+		const repositoryId = url.searchParams.get('repositoryId');
+
+		// Get the appropriate stream based on parameters
+		let stream;
+		if (repositoryId) {
+			stream = broadcaster.subscribeRepository(repositoryId);
+		} else {
+			stream = broadcaster.subscribeAll();
+		}
+
+		return new Response(stream, {
+			headers: {
+				'Content-Type': 'text/event-stream',
+				'Cache-Control': 'no-cache',
+				'Connection': 'keep-alive',
+				'X-Accel-Buffering': 'no',
+				'Access-Control-Allow-Origin': '*'
+			}
+		});
+	} catch (err) {
+		return handleServiceError(err);
+	}
+};
+
+export const OPTIONS: RequestHandler = () => {
+	return new Response(null, {
+		status: 204,
+		headers: {
+			'Access-Control-Allow-Origin': '*',
+			'Access-Control-Allow-Methods': 'GET, OPTIONS',
+			'Access-Control-Allow-Headers': 'Content-Type, Authorization'
+		}
+	});
+};