fix: replace hardcoded IBAN and bank details in placeholders

[TaprootFreak]

Summary

• Replace real account IBAN (CH78 8080 8002 6086 1409 2) with generic placeholder (CH00 0000 0000 0000 0000 0)
• Replace DFX AG and Raiffeisenbank with generic values (Acme AG, Bank)
• Fixes security bot finding from Release: develop -> main #1043 (hardcoded bank details in source code)

Test plan

• Verify placeholder text in manual bank transaction form at /sepa/manual
• Confirm form still validates and submits correctly

[github-actions]

🤖 PR Review Bot

❌ Security: 1 critical vulnerabilities

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