docs: fix JWT auth recipe API errors from review feedback

[Copilot]

Corrects API mismatches in JWT authentication cookbook recipe based on code review feedback for PR #80.

JWT Claims Structure

• Added required exp: usize field to Claims struct (JWT validation fails without it due to validate_exp: true default)
• Removed misleading comment suggesting exp is optional

Token Creation

• Fixed create_token signature: uses 2 parameters (claims, secret), not 3
• Added proper expiration calculation using SystemTime::now() in login handler
• Set exp in Claims before calling create_token

Framework Consistency

• Changed #[tokio::main] → #[rustapi::main] to match other recipes
• Fixed JwtLayer instantiation: JwtLayer::<Claims>::new(secret) with type parameter
• Removed invalid .with_algorithm() call (HS256 is default, use .with_validation() if customization needed)

Minor Fixes

• Fixed typo in quickstart: "This commands sets up" → "This command sets up"

All changes align with actual rustapi-extras v0.1.233 implementation.

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[Copilot]

Pull request overview

This PR corrects API mismatches and improves clarity in the JWT authentication cookbook recipe, ensuring alignment with the actual rustapi-extras v0.1.233 implementation. The changes address technical inaccuracies identified during review of PR #80.

Changes:

• Updated Claims struct comment to clarify that exp field is required for JWT expiration validation (which defaults to enabled)
• Fixed expiration calculation by properly computing the timestamp using SystemTime::now() and storing it in a clearly-named expiration variable before assignment
• Corrected JwtLayer instantiation to use explicit type parameter syntax: JwtLayer::<Claims>::new(secret)

[Copilot]

This import statement is redundant. SystemTime and UNIX_EPOCH are already imported at line 47 at the top of the code block. The inline import should be removed.

Suggested change

use std::time::{SystemTime, UNIX_EPOCH};