fix: resolve module resolution errors by replacing path aliases with relative imports

- Replace all @/ path aliases with proper relative imports and .js extensions
- Update @mollie/api-client peer dependency to support v4.x (^3.7.0 || ^4.0.0)
- Bump version to 0.1.5
- Ensure ESM compatibility for plugin distribution

Fixes module resolution error: "Cannot find package '@/collections'" when using
the plugin in external PayloadCMS projects.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/providers/index.ts

@@ -1,4 +1,4 @@
-export * from './mollie'
-export * from './stripe'
-export * from './types'
-export * from './currency'
+export * from './mollie.js'
+export * from './stripe.js'
+export * from './types.js'
+export * from './currency.js'