Implement tip memo field validation

[Mosas2000]

Type: Bug Fix
Component: Frontend, Backend
Priority: Medium

Description

Tip memo field accepts any length input, causing transaction failures when memo exceeds blockchain limits. Add proper validation and character limits.

Current Behavior

• No character limit on memo field
• Transactions fail with long memos
• Poor error messages

Expected Behavior

• Character limit enforced in UI
• Real-time character count
• Clear validation messages
• Prevent submission of invalid memos

Acceptance Criteria

• Add character limit (e.g., 256 chars)
• Character counter in UI
• Client-side validation
• Server-side validation
• Clear error messages
• Add validation tests