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/lib/types.ts

@@ -32,6 +32,7 @@ export type RepositoryState = 'pending' | 'indexing' | 'indexed' | 'error';
 export type SnippetType = 'code' | 'info';
 export type JobStatus = 'queued' | 'running' | 'done' | 'failed';
 export type VersionState = 'pending' | 'indexing' | 'indexed' | 'error';
+export type EmbeddingProviderKind = 'local-transformers' | 'openai-compatible';
 
 // ---------------------------------------------------------------------------
 // API / service layer types