feat(scripts): support external file embedding

docs/SCRIPTS_COMMAND.md

@@ -85,6 +85,23 @@ migrations/
 
 All files will be found and executed in Priority→Sequence order regardless of directory structure.
 
+## External File Embedding
+
+Script SQL can embed nearby text or binary files before execution using `-- @embed` directives:
+
+```sql
+-- @embed: path=assets/message.txt var=:message mode=text
+-- @embed: path=assets/photo.bin var=:payload mode=base64
+INSERT INTO assets (message, payload)
+VALUES (:message, decode(:payload, 'base64')::bytea);
+```
+
+- `path`: File path resolved relative to the SQL file containing the directive
+- `var`: Named placeholder to replace, such as `:message`
+- `mode`: `text` embeds an escaped SQL string literal; `base64` embeds a base64 string literal
+
+The directive comment is removed from the SQL, and every matching placeholder is replaced before the script is listed or executed.
+
 ## Commands
 
 ### relspec scripts list