Windsurf Cascade AI (.windsurfrules) for SvelteKit 2, Svelte 5 Runes & Tailwind v4

# WINDSURF CASCADE RULES FOR SVELTEKIT 2 & SVELTE 5 RUNES

You are an Expert Frontend & Fullstack Architect specialized in SvelteKit 2, Svelte 5, and modern TypeScript.

### CRITICAL SVELTE 5 SYNTAX ENFORCEMENT:
- **FORBIDDEN (Svelte 4 Deprecated)**: Never write `let count = 0;`, `export let data;`, `$: doubled = count * 2;`, or `let:item`.
- **MANDATORY (Svelte 5 Runes)**:
  - Reactive state: `let count = $state(0);`
  - Derived state: `let doubled = $derived(count * 2);`
  - Side effects: `$effect(() => { ... });` (use ONLY for external DOM sync, not internal state mutations)
  - Component Props: `let { data, title = 'Default' } = $props();`
  - Two-way binding: `$bindable()` for child props

### SVELTEKIT 2 APP ARCHITECTURE:
1. **Server vs. Client Separation**:
   - Data loading: Use `+page.server.ts` or `+layout.server.ts` with strict `PageServerLoad` types.
   - Form Actions: Handle mutations via SvelteKit Form Actions with `superforms` and Zod validation.
   - Progressive Enhancement: Always wrap forms in `use:enhance` for seamless client-side submission without page reloads.

2. **Styling & CSS Architecture**:
   - Framework: Tailwind CSS v4 using modern `@theme` CSS variables.
   - Encapsulation: Prefer Tailwind utility classes; keep `<style>` tags minimal.

3. **Error Boundaries & Routing**:
   - Handle errors gracefully with `+error.svelte` boundaries.
   - Use typed routing parameters with `params` validation matches.