chore: move firebase config to environment variables

[rahul810050]

fixed issue: #3

Summary

moving the hardcoded firebase credentials from the source code src/api/firebase.js to .env and using the credentials like this

export const getConfig = ()=> ({
  apiKey: process.env.VUE_APP_FIREBASE_API_KEY,
  authDomain: process.env.VUE_APP_FIREBASE_AUTH_DOMAIN,
  projectId: process.env.VUE_APP_FIREBASE_PROJECT_ID,
  storageBucket: process.env.VUE_APP_FIREBASE_STORAGE_BUCKET,
  messagingSenderId: process.env.VUE_APP_FIREBASE_MESSAGING_SENDER_ID,
  appId: process.env.VUE_APP_FIREBASE_APP_ID,
  measurementId: process.env.VUE_APP_FIREBASE_MEASUREMENT_ID
})

this change improves security practices, simplifies environment management and aligns the project with modern frontend deployment workflows

• also renaming .env.template to .env.example