feat: Add contribution guidelines and update project files

This commit introduces guidelines for contributors and makes several project updates:

- **Contribution Guidelines**:
    - Adds `CONTRIBUTING.md` with instructions on how to contribute, coding guidelines, and the pull request process.
    - Adds `CODE_OF_CONDUCT.md` based on the Contributor Covenant.
- **README Update**:
    - Removes the "Contributing" section, deferring to `CONTRIBUTING.md`.
    - Adds a "Roadmap" section outlining future plans for the project.
- **Version Increment**:
    - Increments the project version in `version.txt` from `1.0.1` to `1.0.2`.
- **Build Configuration**:
    - Enables signing for the release build type in `app/build.gradle.kts` using the debug signing config.