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/message.surql

@@ -0,0 +1,19 @@
+# Defines the schema for the 'message' table.
+
+DEFINE TABLE IF NOT EXISTS message SCHEMALESS;
+
+# Standard fields
+DEFINE FIELD IF NOT EXISTS created_at ON message TYPE datetime;
+DEFINE FIELD IF NOT EXISTS updated_at ON message TYPE datetime;
+
+# Custom fields from the Message struct
+DEFINE FIELD IF NOT EXISTS conversation_id ON message TYPE string;
+# MessageRole is an enum, store as string
+DEFINE FIELD IF NOT EXISTS role ON message TYPE string;
+DEFINE FIELD IF NOT EXISTS content ON message TYPE string;
+# references is Option<Vec<String>>, store as array<string>
+DEFINE FIELD IF NOT EXISTS references ON message TYPE option<array<string>>;
+
+# Indexes based on query patterns (get_complete_conversation)
+DEFINE INDEX IF NOT EXISTS message_conversation_id_idx ON message FIELDS conversation_id;
+DEFINE INDEX IF NOT EXISTS message_updated_at_idx ON message FIELDS updated_at; # For ORDER BY