[frontend] Shared MissionCard component

[Kaylahray]

Description

Extract a reusable MissionCard component used on both the hunter mission board and creator dashboard.

User Story

As a developer,
I want to share one mission card component,
so that mission displays stay consistent and are easier to maintain.

Requirements and Context

• New file: src/components/missions/MissionCard.tsx
• Props: title, reward, participants, status, href, optional assetGate
• Replace duplicate card markup in hunter and creator features
• Use StatusBadge from [frontend] Mission status badges across UI

Suggested Implementation

// IN FILE: src/components/missions/MissionCard.tsx
// 1. Define MissionCardProps interface.
// 2. Render card with title, reward, slots, StatusBadge.
// 3. Wrap in Link when href provided.

Acceptance Criteria

• Single MissionCard component exists.
• Used on mission board and creator quest list.
• Visual style consistent across both contexts.

Submission Guidelines

• Branch: frontend/shared-mission-card
• Depends on: [frontend] Mission status badges across UI, [frontend] Mission board page
• PR: refactor(frontend): extract shared MissionCard component