fix: secure session handling and landing page redirect

[Vasist10]

Description

• Increase session cookie lifetime to 30 days.

• Fix secure cookie handling behind ingress using dynamic Secure flag and helper save function.

• Inject authenticated user credentials into request headers/body using AuthMiddleware so handlers always receive correct user info.

• Fixes: I have to log in all the time #417

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

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