Add first bot onboarding tutorial

[pepperfm]

Summary

• Adds an end-to-end first bot onboarding tutorial covering installation, BotFather setup, webhook registration, /start handling, chat registration, first message sending, and tests.
• Adds a dedicated troubleshooting page for token, webhook, secret, chat registration, config cache, and local tunnel issues.
• Links the tutorial and troubleshooting guide from quickstart, webhook, and testing documentation.
• Keeps the new user-facing documentation in English and reuses existing screenshots with relative paths and alt text.

Validation

• composer validate
• vendor/bin/pest tests/Feature/Docs/FirstBotTutorialTest.php tests/Feature/DocumentationCodeSnippetsTest.php
• git diff --cached --check
• checked that README, docs, and touched feature tests contain no Cyrillic text

Closes #232

[pepperfm]

@MarioGattolla 🙏

[MarioGattolla]

Hi @pepperfm Thank you for your merge request. Due to the large number of changes, it will take a few days to review it. I'm working on it