fix: correct contract index validation and wire up in Send page

[alez04]

Problem

Contract index validation in ValidateDestination() was capping out at 23, but mainnet already has 27 deployed contracts. The lower bound was also incorrect—indices start at 1, not 0.

Additionally, during this audit it was discovered that ValidateDestination() wasn't actually being utilized for the Send feature. The Send page had its own hardcoded length check (.Length != 60) that prevented contract indices from being entered, and AllowContractIndex was disabled on the input component.

Fix

• Widened the accepted range to 1–1023 to match ScAuctions.razor and protocol specifications.
• Wired up the Send page to support contract index inputs by enabling AllowContractIndex="true".
• Added a ResolveIdentity helper to cleanly convert the input string (whether a 60-character address or a short contract index) into a valid QubicIdentity before signing.
• Updated Send.razor to use the correct validation and resolution paths.