docs: replace complex tutorial with 3 simple contact form examples

Examples:
1. Contact Form → Telegram + Slack (direct fan-out)
2. Contact Form → PostgreSQL → CDC → Telegram (CDC-driven)
3. Contact Form → Email + Slack (confirmation + notification)

Each includes a runnable shell script and test commands.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: vsilent