Add Validation for `htmlReloadMethod` Config

[taeyang91]

Hey there! First off, thanks for all the hard work on this awesome gem.

Right now, the default value for htmlReloadMethod is :morph, and you can change it to :replace. But I ran into a problem when I was switching between them (accidentally misspelled :morph). The gem just defaulted to :replace without me realizing it instead of failing or warning. Took me a while to figure out what was going on.

I get that since :morph is the default, most users probably won’t be setting it manually but silently falling back to :replace without any error or warning might not be ideal.

It'd be helpful to add some kind of config validation to catch typos or invalid values. Maybe:

1. Raise an error if the value isn’t :morph or :replace.
2. Log a warning so at least there’s some feedback.

Curious what you think.