Fix WASM memory error in isValidAccountName

gandalf_automationrequested to merge
fix/wasm-username-validation into develop

Summary

Fixes server crash when WASM isValidAccountName fails with memory error under concurrent load.

Problem

WaxError: Non-typed Error during Wasm call: RuntimeError: memory access out of bounds

This causes 500 errors on routes like /notifications.

Solution

Add try-catch around WASM call with regex fallback validation.

Follow-up TODOs (separate tasks)

  • Verify regex matches blockchain consensus rules
  • Create test to reproduce WASM issue
  • Add HAF API endpoint for server-side validation

Testing

  • Verify notifications page loads
  • Verify account validation still works

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