Crypto Map not loading in some browser

[onmax]

Show fallback placeholder if Crypto Map iframe fails to load

Some users (e.g. using Brave or with ad blockers enabled) may not see the Crypto Map because the iframe is blocked. In these cases, we should display a placeholder message or image instead.

Related: #6

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What to do:

• Detect if the iframe fails to load (e.g. onerror or timeout-based fallback).
• Show a clear, non-intrusive placeholder in its place—something like:
  "Crypto Map couldn't load. This may be due to an ad blocker or network restrictions."

Why:

• Ensures a smoother user experience when the iframe is blocked.

Done when:

• Placeholder is shown reliably when the iframe doesn't load.
• Tested with Brave and common ad blockers (uBlock, Adblock Plus).
• Layout remains visually consistent with and without the iframe.