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/repos/[id]/+page.svelte

@@ -75,6 +75,18 @@
 		error: 'Error'
 	};
 
+	const stageLabels: Record<string, string> = {
+		queued: 'Queued',
+		differential: 'Diff',
+		crawling: 'Crawling',
+		cloning: 'Cloning',
+		parsing: 'Parsing',
+		storing: 'Storing',
+		embedding: 'Embedding',
+		done: 'Done',
+		failed: 'Failed'
+	};
+
 	async function refreshRepo() {
 		try {
 			const res = await fetch(`/api/v1/libs/${encodeURIComponent(repo.id)}`);
@@ -105,63 +117,78 @@
 		loadVersions();
 	});
 
-	// Single shared poller — one interval regardless of how many tags are active.
-	// This replaces the N per-version <IndexingProgress> components that each had
-	// their own setInterval, which caused ERR_INSUFFICIENT_RESOURCES and UI lockup
-	// when hundreds of tags were queued simultaneously.
+	// Single shared poller replaced with EventSource SSE stream
 	$effect(() => {
-		const activeIds = new Set(
-			Object.values(activeVersionJobs).filter((id): id is string => !!id)
-		);
-		if (activeIds.size === 0) {
-			versionJobProgress = {};
-			return;
-		}
+		if (!repo.id) return;
 
 		let stopped = false;
+		const es = new EventSource(
+			`/api/v1/jobs/stream?repositoryId=${encodeURIComponent(repo.id)}`
+		);
 
-		async function poll() {
+		es.addEventListener('job-progress', (event) => {
 			if (stopped) return;
 			try {
-				const res = await fetch(
-					`/api/v1/jobs?repositoryId=${encodeURIComponent(repo.id)}&limit=1000`
-				);
-				if (!res.ok || stopped) return;
-				const d = await res.json();
-
-				// Build a jobId → job lookup from the response.
-				const map: Record<string, IndexingJob> = {};
-				for (const job of (d.jobs ?? []) as IndexingJob[]) {
-					map[job.id] = job;
-				}
-				if (!stopped) versionJobProgress = map;
-
-				// Retire completed jobs and trigger a single refresh.
-				let anyCompleted = false;
-				const nextJobs = { ...activeVersionJobs };
-				for (const [tag, jobId] of Object.entries(activeVersionJobs)) {
-					if (!jobId) continue;
-					const job = map[jobId];
-					if (job?.status === 'done' || job?.status === 'failed') {
-						delete nextJobs[tag];
-						anyCompleted = true;
-					}
-				}
-				if (anyCompleted && !stopped) {
-					activeVersionJobs = nextJobs;
-					void loadVersions();
-					void refreshRepo();
-				}
+				const data = JSON.parse(event.data) as IndexingJob;
+				versionJobProgress = { ...versionJobProgress, [data.id]: data };
 			} catch {
-				// ignore transient errors
+				// ignore parse errors
 			}
-		}
+		});
+
+		es.addEventListener('job-done', (event) => {
+			if (stopped) return;
+			try {
+				const data = JSON.parse(event.data) as IndexingJob;
+				const next = { ...versionJobProgress };
+				delete next[data.id];
+				versionJobProgress = next;
+				void loadVersions();
+				void refreshRepo();
+			} catch {
+				// ignore parse errors
+			}
+		});
+
+		es.addEventListener('job-failed', (event) => {
+			if (stopped) return;
+			try {
+				const data = JSON.parse(event.data) as IndexingJob;
+				const next = { ...versionJobProgress };
+				delete next[data.id];
+				versionJobProgress = next;
+				void loadVersions();
+				void refreshRepo();
+			} catch {
+				// ignore parse errors
+			}
+		});
+
+		es.onerror = () => {
+			if (stopped) return;
+			es.close();
+			// Fall back to a single fetch for resilience
+			(async () => {
+				try {
+					const res = await fetch(
+						`/api/v1/jobs?repositoryId=${encodeURIComponent(repo.id)}&limit=1000`
+					);
+					if (!res.ok || stopped) return;
+					const d = await res.json();
+					const map: Record<string, IndexingJob> = {};
+					for (const job of (d.jobs ?? []) as IndexingJob[]) {
+						map[job.id] = job;
+					}
+					if (!stopped) versionJobProgress = map;
+				} catch {
+					// ignore errors
+				}
+			})();
+		};
 
-		void poll();
-		const interval = setInterval(poll, 2000);
 		return () => {
 			stopped = true;
-			clearInterval(interval);
+			es.close();
 		};
 	});
 
@@ -620,7 +647,10 @@
 						{@const job = versionJobProgress[activeVersionJobs[version.tag]!]}
 						<div class="mt-2">
 							<div class="flex justify-between text-xs text-gray-500">
-								<span>{(job?.processedFiles ?? 0).toLocaleString()} / {(job?.totalFiles ?? 0).toLocaleString()} files</span>
+							<span>
+								{#if job?.stageDetail}{job.stageDetail}{:else}{(job?.processedFiles ?? 0).toLocaleString()} / {(job?.totalFiles ?? 0).toLocaleString()} files{/if}
+								{#if job?.stage}{' - ' + stageLabels[job.stage] ?? job.stage}{/if}
+							</span>
 								<span>{job?.progress ?? 0}%</span>
 							</div>
 							<div class="mt-1 h-1.5 w-full rounded-full bg-gray-200">