[Medium] Add vaccination proof generation UI

[Josie123-Dev]

Task Description

Create vaccination proof generation interface:

• Select vaccination credential
• Choose proof parameters
• Generate proof
• Show proof status
• Display generated proof

Requirements

• Credential selection
• Parameter configuration
• Proof generation
• Status display
• Proof visualization

Acceptance Criteria

• Selection works
• Parameters are configurable
• Generation works
• Status is shown
• Proof is displayed

[waterWang]

Implemented vaccination proof generation UI in PR #157: credential selection, parameter configuration, generated proof display with verification hash, copy/download. 51/51 tests passing.