chore: harden common storage bootstrap and slim embedded db assets

Unify embedding config, build providers from system settings, and fail
startup when index builds error or time out. Move Surreal assets under
common/db so embeds exclude crate source, and read storage via streams.

common/db/migrations/20251121_113122_migrate_embedding_data.surql

@@ -0,0 +1,23 @@
+-- Copy embeddings from base tables to dedicated tables
+-- This runs BEFORE the field removal migration
+
+FOR $chunk IN (SELECT * FROM text_chunk WHERE embedding != NONE AND array::len(embedding) > 0) {
+    CREATE text_chunk_embedding CONTENT {
+        chunk_id: $chunk.id,
+        embedding: $chunk.embedding,
+        user_id: $chunk.user_id,
+        source_id: $chunk.source_id,
+        created_at: $chunk.created_at,
+        updated_at: $chunk.updated_at
+    };
+};
+
+FOR $entity IN (SELECT * FROM knowledge_entity WHERE embedding != NONE AND array::len(embedding) > 0) {
+    CREATE knowledge_entity_embedding CONTENT {
+        entity_id: $entity.id,
+        embedding: $entity.embedding,
+        user_id: $entity.user_id,
+        created_at: $entity.created_at,
+        updated_at: $entity.updated_at
+    };
+};