Fix authorization middleware

[Hell1213]

Fixed critical security vulnerability where task endpoints accepted user credentials directly from requests without validating authenticated sessions, allowing unauthorized access to any user's tasks.

Fixes: #338

Changes Made
Added authentication middleware to validate user sessions
Created credential validation helpers to verify request params match session
Updated all 8 task endpoints to use session-based authentication
Integrated middleware protection for all task operations

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

All task endpoints now require valid session before processing. Request credentials are validated against session data. Returns 401 for missing session, 403 for credential mismatch. Backward compatible with existing frontend.

[github-actions]

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[Hell1213]

Added session validation middleware

[Hell1213]

added tests for middleware validation

[Hell1213]

implemented creds validation helpers

[Hell1213]

added tests for helper functions

[Hell1213]

using session creds for bulk operations

[Hell1213]

wrapped all task endpoints with auth middleware

[Hell1213]

backend/controllers/get_tasks.go - Use session credentials instead of request params
backend/controllers/add_task.go - Use session credentials instead of request params
backend/controllers/edit_task.go - Use session credentials instead of request params
backend/controllers/modify_task.go - Use session credentials instead of request params
backend/controllers/complete_task.go - Use session credentials instead of request params
backend/controllers/delete_task.go - Use session credentials instead of request params

backend/controllers/delete_tasks.go - Use session credentials for bulk operations

[Hell1213]

hey @its-me-abhishek PR ready for review, fixed: Session-based authorization for task endpoints.
please let me know if any changes needed !