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/schemas/conversation.surql

@@ -0,0 +1,16 @@
+# Defines the schema for the 'conversation' table.
+
+DEFINE TABLE IF NOT EXISTS conversation SCHEMALESS;
+
+# Standard fields
+DEFINE FIELD IF NOT EXISTS created_at ON conversation TYPE datetime;
+DEFINE FIELD IF NOT EXISTS updated_at ON conversation TYPE datetime;
+
+# Custom fields from the Conversation struct
+DEFINE FIELD IF NOT EXISTS user_id ON conversation TYPE string;
+DEFINE FIELD IF NOT EXISTS title ON conversation TYPE string;
+
+# Add indexes based on query patterns (get_complete_conversation ownership check, get_user_conversations)
+DEFINE INDEX IF NOT EXISTS conversation_user_id_idx ON conversation FIELDS user_id;
+DEFINE INDEX IF NOT EXISTS conversation_created_at_idx ON conversation FIELDS created_at; # For get_user_conversations ORDER BY
+DEFINE INDEX IF NOT EXISTS conversation_user_updated_at_idx ON conversation FIELDS user_id, updated_at; # For sidebar conversation projection ORDER BY