feat(EMBEDDINGS-0001): enable local embedder by default and overhaul settings page

- Wire local embedding provider as the default on startup when no profile is configured
- Refactor embedding settings into dedicated service, DTOs, mappers and models
- Rebuild settings page with profile management UI and live test feedback
- Expose index summary (indexed versions + embedding count) on repo endpoints
- Harden indexing pipeline and context search with additional test coverage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/api/v1/libs/[id]/+server.ts

@@ -23,7 +23,7 @@ export const GET: RequestHandler = ({ params }) => {
 			return json({ error: 'Repository not found', code: 'NOT_FOUND' }, { status: 404 });
 		}
 		const versions = service.getVersions(id);
-		return json({ ...RepositoryMapper.toDto(repo), versions });
+		return json({ ...RepositoryMapper.toDto(repo), versions, ...service.getIndexSummary(id) });
 	} catch (err) {
 		return handleServiceError(err);
 	}