docs: update tap to pay page - remove email and add testing section

[devin-ai-integration]

Summary

Three small updates to the Tap to Pay wallet integration guide (payments/wallets/tap-to-pay.mdx):

1. Updated contact note wording — Replaced [contact us](mailto:wallets@walletconnect.com) with plain text "reach out to our team" (no email link).
2. Added a Testing section — New section at the bottom of the page directing wallet developers to the Demo POS App for testing, noting that an Android device is required and access must be requested.

Review & Testing Checklist for Human

• Verify the Note at the top renders correctly with the new wording: "…reach out to our team before getting started." — no hyperlink should be present
• Verify the new "Testing" section appears at the bottom of the page after both the Android and iOS integration steps

Notes

• Pure content changes — no structural or config modifications.

Link to Devin session: https://app.devin.ai/sessions/6941d7de6bd54801a8caea685334a652
Requested by: @mirnab0

[devin-ai-integration]

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