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/lib/types.ts

@@ -31,6 +31,7 @@ export type RepositorySource = 'github' | 'local';
 export type RepositoryState = 'pending' | 'indexing' | 'indexed' | 'error';
 export type SnippetType = 'code' | 'info';
 export type JobStatus = 'queued' | 'running' | 'done' | 'failed';
+export type IndexingStage = 'queued' | 'differential' | 'crawling' | 'cloning' | 'parsing' | 'storing' | 'embedding' | 'done' | 'failed';
 export type VersionState = 'pending' | 'indexing' | 'indexed' | 'error';
 export type EmbeddingProviderKind = 'local-transformers' | 'openai-compatible';