feat: guidelines: add Inertia form guidelines

[ashleyhindle]

What & Why

Inertia released a new <Form> component which makes building forms a lot easier. We want Boost to help AI/users make use of this component, when it's available.

Core

• Adds initial conditional Inertia form guidelines 🙌 Trying to be mindful of versions, how new <Form> is, and existing project conventions
• Adds basic Svelte Inertia guidelines

Extra

• Adds special Inertia GuidelineAssist class to conditionally include guidelines
• Adds @boostsnippet directive to simplify adding verbatim code snippets without accidentally running PHP code or Vue {{ errors.name }} code being ran

How I tested

Building a feature

1. Created new Inertia project using Boost via local path in composer.json
2. Ran boost:install, checked the resulting guidelines
3. Asked AI to build me forms
   Prompt example:

Can we add a basic form to the homepage @routes/web.php for "Preferred things?" with different questions using different input options (input, select, radio, checkbox, etc..), and on submit we just show a nice markdown file of their preferences?

Manually reading

1. php all.php > all.md; open all.md to read through all guidelines
2. ./artisan boost:install; less CLAUDE.md to read through guidelines for this specific test project

Notes/thoughts

• I did try to add indention removal so conditionals are cleaner (i.e. .ai/inertia-laravel/2/core.blade.php), but when we want indented lists it's problematic. Have to revisit this.
  • In future we might need the ability to conditionally include whole files. React's 'forms.blade.php' is a bit messy with the conditionals being so big, but what if it was just: @if(hasForms()) @include('.forms-with-component.blade.php') @else @include('.forms-without-component.blade.php')? Then we can keep the guidelines separately managed, and instead conditionally include the entire file.
    • This just requires those files to not be auto-included by the composer, so we'd need some exclusion logic there, which is for a future PR.
• I wanted to check existing Inertia files to see if <Form> is in use, then we can strengthen the language and exclude the useForm part, but that's extra tricky for v1, I think that's a v2 thing.
  • We have to be careful with our language in the guidelines here, as 99% of people aren't using <Form> yet, so we can't enforce that usage bringing their codebase out of alignment.

Demo

CleanShot.2025-08-27.at.15.18.26.mp4