Bump dependencies & introduce Dependabot for automated updates

[msbelaid]

Summary

Manually update Kotlin, Gradle, Coil, Koin, and other outdated dependencies, then introduce a Dependabot configuration to automate future dependency update PRs.

Checklist

Ensure all of the following pass before merging:

• Debug build
• Release build
• Unit tests
• Ktlint
• Screenshot tests
• UI tests

Dependabot Configuration

• Weekly schedule (Mondays)
• Gradle and GitHub Actions ecosystems both covered
• Dependencies grouped by ecosystem (AndroidX, Compose, Kotlin, Koin, Coil…)
• Major version bumps ignored for AGP
• Meaningful labels added (dependencies, android, ci)
• Conventional commit prefix set (chore for deps, ci for actions)
• Branch protection rule requires CI to pass before Dependabot PRs can merge