defineModuleConfig: Pages/Index.tsx silently breaks builds on case-insensitive filesystems

[antosubash]

A module whose only page is Pages/Index.tsx (with the framework-required Pages/index.ts barrel doing () => import('./Index')) builds a broken bundle on macOS/Windows.

Repro (macOS or Windows)

1. Module with single page Pages/Index.tsx and barrel Pages/index.ts:

   export const pages = { 'Foo/Index': () => import('./Index') };

2. vite build succeeds, no warnings.
3. The lazy chunk emitted (Index-<hash>.mjs) contains the barrel's content (~94 bytes), not the React component:

   var pages = { "Foo/Index": () => import("./Index-<hash>.mjs") };
   export { pages };

   (recursive self-import)
4. Runtime: TypeError: Cannot assign to property 'layout' of [object Module] from resolveLayout — the lazy import returned the frozen entry namespace, not a component module.

Cause

Rolldown resolves import('./Index') to ./index.ts (the entry) on case-insensitive filesystems. The build silently produces a duplicated chunk. Workaround in consumer code is import('./Index.tsx') with explicit extension.

Fix options

1. defineModuleConfig rejects this combination at config-evaluation time with a clear error.
2. Auto-rewrite extension-less imports inside Pages/index.ts (similar to TypeScript module: "node16").
3. Rename the framework barrel to something that can't collide (e.g. Pages/_pages.ts).

The natural pattern for any module's "home" page IS Pages/Index.tsx, so this trap will catch every new framework adopter on Mac/Windows.

[antosubash]

Resolved by #139.

packages/SimpleModule.Client/src/define-module-config.ts now calls assertNoBarrelCollision(dir) at config evaluation time. It detects the Pages/index.ts + Pages/Index.tsx barrel/page collision combined with an extension-less import('./Index') and throws an actionable error pointing the developer at the fix (use the explicit extension or rename the page).

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