[❗ Enhancement] Repository Improvements

It's about time to actually improve this repository.

# Emoji key

Emoji | Description
:---:|---
:exclamation: | The task has a high priority
:construction: | The task is currently being worked on
:negative_squared_cross_mark: | The task will not be worked on
:clock9: | The task will be delayed until further notice
:link: | The task has a linked PR/commit

# Tasks

## Maintainer improvements

- [ ] Add issue templates
- [ ] Bug reports
- [ ] Feature requests/enhancements
- [ ] UX/UI requests/enhancements
- [ ] Other templates (if necessary)
- [ ] Add contributing guide
- [ ] Expected commit/contributing standards
- [ ] Indicate how to run the app locally
- [ ] Handle issues/PRs from first-time users
- [ ] Review repository labels [:construction:]

## Existing issues/PRs

- [ ] Work on outstanding issues [:clock9:]
- [ ] Merge outstanding PRs [:clock9:]

## Continuous Integration

- [ ] Add initial GitHub Actions [:construction:]
- [x] Unit testing (introduced with 7af5da8f64328339bd149a6cf4e239426338e8ed)
- [ ] Deploy to Firebase
- [x] Stale issues/PRs (introduced with 7af5da8f64328339bd149a6cf4e239426338e8ed)
- [x] Code scanning (introduced with 7af5da8f64328339bd149a6cf4e239426338e8ed)

## Other

- [ ] Improve repository transparency
- [ ] Add updates document to the wiki/repository
- [ ] Add initial help guides
- [ ] Invite maintainers?