[Feature Request]: Display Codeforces avatar on Profile and create reusable Empty State component

[Sandesh282]

Description:

This issue addresses two related UI improvements: loading the user's actual Codeforces avatar on the Profile screen, and creating a shared EmptyStateView component to standardize how empty, error, and loading states are presented across all screens.

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Part A: Profile Avatar

Current Behavior:

The profile header uses a placeholder SF Symbol (person.fill), even though:

• The Codeforces user.info API returns an avatar URL (titlePhoto / avatar field).
• SDWebImageSwiftUI is already imported in ProfileView.swift but is never used.

Feature Requirements:

• Add avatar and titlePhoto fields to the CodeforcesUser model in ProfileModels.swift.
• Replace the placeholder icon in profileHeader() with a WebImage from SDWebImageSwiftUI that loads the actual avatar.
• Provide a fallback to the existing SF Symbol if the image URL is nil or fails to load.
• Retain the existing circular shape with gradient border styling.

Note: Codeforces avatar URLs are often protocol-relative (e.g., //userpic.codeforces.org/...). Prepend https: before using them.

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Part B: Reusable Empty State Component

Current Behavior:

Empty, error, and loading states are handled inconsistently across the app:

Screen	Implementation
ContestListView	Plain ProgressView() with no empty results or error state
ProblemListView	Custom VStack with icon and retry button
ProfileView	Raw error text string
ProblemSubmissionsView	ContentUnavailableView (iOS 17+ only)

Feature Requirements:

• Create a reusable EmptyStateView in CForge/Views/Common/EmptyStateView.swift with configurable icon, title, subtitle, and optional action button.
• Style it with the app's neon dark theme (gradient icon, .textPrimary title, gradient action button).
• Replace all inconsistent empty/error/loading state implementations across ContestListView, ProblemListView, ProfileView, and ProblemSubmissionsView with the shared component.

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Steps to Implement:

Part A:

1. Add avatar: String? and titlePhoto: String? to CodeforcesUser in ProfileModels.swift.
2. In ProfileView.profileHeader(), replace the SF Symbol with WebImage(url:) from SDWebImageSwiftUI.
3. Add a .placeholder { ... } modifier for fallback.
4. Ensure the avatar retains circular clipping and the gradient border overlay.

Part B:

1. Create CForge/Views/Common/EmptyStateView.swift with a configurable initializer.
2. Apply the neon theme: gradient-colored SF Symbol icon, proper text hierarchy, optional neon-styled retry button.
3. Replace empty/error states in ContestListView, ProblemListView, ProfileView, and ProblemSubmissionsView.
4. Optionally update the existing LoadingView.swift to match the new design.

Key Files:

Action	File
MODIFY	CForge/Views/Profile/ProfileModels.swift
MODIFY	CForge/Views/Profile/ProfileView.swift
CREATE	CForge/Views/Common/EmptyStateView.swift
MODIFY	CForge/Views/Contest/ContestListView.swift
MODIFY	CForge/Views/Problem/ProblemListView.swift
MODIFY	CForge/Views/Problem/ProblemSubmissionsView.swift

Expected Outcome:

• The Profile screen displays the user's actual Codeforces avatar with a graceful fallback.
• All screens use the shared EmptyStateView for consistent empty, error, and loading presentations.
• The UI across the entire app feels polished and unified.

[mvanhorn]

Opened a PR for this in #14.

Bundled both parts in one PR (avatar load + reusable EmptyStateView sweep across four screens). Happy to split into 9a (avatar) and 9b (EmptyStateView refactor) if you'd prefer smaller review units - just let me know.