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

package.json

@@ -5,7 +5,7 @@
 	"type": "module",
 	"scripts": {
 		"dev": "vite dev",
-		"build": "vite build",
+		"build": "vite build && node scripts/build-workers.mjs",
 		"preview": "vite preview",
 		"prepare": "svelte-kit sync || echo ''",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
@@ -34,6 +34,7 @@
 		"@vitest/browser-playwright": "^4.1.0",
 		"drizzle-kit": "^0.31.8",
 		"drizzle-orm": "^0.45.1",
+		"esbuild": "^0.24.0",
 		"eslint": "^9.39.2",
 		"eslint-config-prettier": "^10.1.8",
 		"eslint-plugin-svelte": "^3.14.0",