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/auth.surql

@@ -0,0 +1,6 @@
+# Defines authentication scope and access rules.
+# This mirrors the logic previously in SurrealDbClient::setup_auth
+
+DEFINE ACCESS IF NOT EXISTS account ON DATABASE TYPE RECORD
+    SIGNUP ( CREATE user SET email = $email, password = crypto::argon2::generate($password), anonymous = false, user_id = $user_id) # Ensure user_id is provided if needed
+    SIGNIN ( SELECT * FROM user WHERE email = $email AND crypto::argon2::compare(password, $password) );