Document the Usage & APIs of `@asgardeo/browser` & `@asgardeo/express`

### Current Limitation

Asgardeo provides SDKs for multiple runtimes and frameworks, including
`@asgardeo/browser` and `@asgardeo/express`. However, the documentation for these SDKs is currently incomplete.

At the moment:
- Vanilla JavaScript applications are expected to use the Browser SDK
https://wso2.com/asgardeo/docs/quick-starts/javascript/
- Express.js applications are expected to use the Express SDK
https://wso2.com/asgardeo/docs/complete-guides/expressjs/introduction/

While the guides reference these SDKs conceptually, there is:
- No clear, up-to-date usage documentation for `@asgardeo/browser`
- No consolidated usage and API documentation for `@asgardeo/express`
- API reference documentation exists only for the React and Next.js SDKs

This makes it difficult for developers to:
- Discover available APIs
- Understand recommended usage patterns
- Build framework-agnostic or server-based integrations with confidence

### Suggested Improvement

Introduce comprehensive **Usage Guides** and **API Documentation** for both
`@asgardeo/browser` and `@asgardeo/express`.

This should include:

#### Browser SDK (`@asgardeo/browser`)
- Clear positioning as the recommended SDK for vanilla JavaScript applications
- Installation and initialization examples
- Common authentication flows (sign-in, sign-out, token handling)
- API reference documentation aligned with existing React/Next.js SDK docs

#### Express SDK (`@asgardeo/express`)
- Clear positioning as the recommended SDK for Express.js applications
- Setup and configuration guide
- Middleware usage patterns
- Server-side authentication flows
- API reference documentation aligned with existing React/Next.js SDK docs

Where possible, the documentation structure and API references should follow the same conventions used for the React and Next.js SDKs to ensure consistency across the SDK suite.

### Please select the package issue is related to

@asgardeo/express, @asgardeo/browser

### Version

N/A

### Reporter Checklist

- [x] I have searched the existing issues and this is not a duplicate.
- [x] I have provided all the necessary information.
- [x] I have verified the improvement is not available in the latest version of the package.