Thread arguments through Compose tree instead of storing in Container

[VictorB00]

Summary

• Moves arguments out of the Container object and threads it through the Compose tree as a parameter, following unidirectional data flow
• Renames initWith(arguments) to makeContainer() — containers are now argument-agnostic
• Makes formRepository non-nullable in ContainerImpl, eliminating null-safe calls
• Wraps trigger modal stacks in key(stack.id) for correct Compose recomposition identity
• Changes remember keys from arguments to stable identifiers (id, componentId, data) so containers aren't recreated on argument changes

Test plan

• Verify embeddings render correctly with arguments passed through the Compose tree
• Confirm form state is preserved when arguments change (container no longer recreated)
• Test trigger modals open/close correctly with the new key(stack.id) wrapping
• Verify template variables still resolve arguments in createVariableForTemplate