Update welcome message and FAQ with iPhone app

[wtfloris]

Summary

• Add hestia.bot and iPhone App Store links to Telegram welcome message (converted to MarkdownV2)
• Update "Can I use Hestia without Telegram?" FAQ answer from "No" to "Yes!" with links to website and app
• Add "Is there an app?" FAQ entry to web version (HTML + EN/NL translations)
• Update iOS browser notification tooltip to link to the app instead of "working on it"

Test plan

• Send /start to the Telegram bot and verify MarkdownV2 renders correctly with clickable links
• Verify FAQ renders correctly in Telegram (/faq)
• Check web FAQ shows the new "Is there an app?" entry in both EN and NL
• Verify iOS notification tooltip shows the App Store link

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