Add initial agent guidelines for generating migrations

Author: codedmonkey

migrations/AGENTS.md

@@ -0,0 +1,18 @@
+# Agent guidelines for Dirigent development: migrations/
+
+## Generate new migrations
+
+To generate a new migration, execute the `symfony console doctrine:migrations:diff --nowdoc --formatted` command.
+
+## Coding style
+
+- Every migration must have a non-empty description.
+- Queries should be wrapped in nowdoc by default. Only if a PHP variable is used in the query is it allowed to be wrapped in heredoc.
+
+## Required columns
+
+If a required (non-nullable) column is added to the schema, add it with the following queries:
+
+1. Add a nullable column.
+2. Set a default value for every row in the table.
+3. Remove the nullable flag from the column.

migrations/CLAUDE.md

@@ -0,0 +1,3 @@
+# Agent guidelines for Dirigent development in Claude Code: migrations/
+
+@AGENTS.md