Recreate alias for php in Dockerfile

[edubarr]

Summary

• Restore the php alias to point to php85.
• Re-add behavior that was introduced in build: create an alias for php #196 but was removed in faed4f8.

Why

• Keep the expected php command available.
• Some tools, such as Composer, expect a php binary to be present.
• Avoid regressing behavior that had already been added before.

Notes

• This only restores the alias; it does not change the PHP version or runtime behavior.