Refactor indexer configuration and improve array source handling

- Add proper foreach loop to handle array sources in Indexer::index()
- Simplify loadSource() to handle single source only
- Move options array shape to IndexerInterface
- Remove loader and transformer from public options API
- Add FeedLoader to blog indexer configuration
- Remove Embedder dependency from EmbedCommand
- Remove default indexer configuration
- Clean up trailing blank line in ai.yaml

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: OskarStark

src/store/src/Indexer.php

@@ -35,9 +35,6 @@ public function __construct(
     ) {
     }
 
-    /**
-     * @param array{chunk_size?: int, loader?: array<string, mixed>, transformer?: array<string, mixed>} $options
-     */
     public function index(null|string|array $source = null, array $options = []): void
     {
         $this->logger->debug('Starting document processing', ['source' => $source, 'options' => $options]);

src/store/src/IndexerInterface.php

@@ -22,7 +22,7 @@ interface IndexerInterface
      * Process sources through the complete document pipeline: load → transform → vectorize → store.
      * 
      * @param null|string|array<string> $source  Source identifier (file path, URL, etc.), array of sources, or null if the loader does not need a source, e.g. InMemoryLoader
-     * @param array<string, mixed> $options Processing options
+     * @param array{chunk_size?: int} $options Processing options
      */
     public function index(null|string|array $source = null, array $options = []): void;
 }