[Good First Issue] Add a CHANGELOG.md documenting project milestones

[kamsirichard]

Context

ScoutBot has shipped a lot since it started — the WhatsApp engine, V2 frontend, Telegram notifications, 507 subscribers, mobile email improvements, and more. None of it is documented in a changelog. Contributors and users have no easy way to see how the project has grown.

Task

Create a CHANGELOG.md in the repo root. Document the major milestones, releases, and improvements in reverse-chronological order.

Format

Use Keep a Changelog format:

# Changelog

## [Unreleased]

## [June 2026]
### Added
- Telegram digest channel (@ScoutBotOpportunities)
- --dry-run flag for email preview without sending
- Mobile-responsive email template
- Auto-label workflow for new issues
- CONTRIBUTORS.md with contributor profiles
...

Source material

• The closed PRs list: https://github.com/TechHub-Extensions/ScoutBot/pulls?q=is%3Apr+is%3Aclosed
• The commit history
• CONTRIBUTORS.md

Good for

Writers and developers alike. No coding required. Estimated time: 1–2 hours.