feat(sharing): implement unified sharing system for social media

Replace old ProgressCardGenerator with protocol-based sharing architecture
supporting trips, achievements, and stadium progress. Features 8 color
themes, Instagram Stories optimization (1080x1920), and reusable card
components with map snapshots.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Export/Sharing/ProgressCardGenerator.swift

@@ -0,0 +1,115 @@
+//
+//  ProgressCardGenerator.swift
+//  SportsTime
+//
+//  Generates shareable stadium progress cards.
+//
+
+import SwiftUI
+import UIKit
+
+// MARK: - Progress Share Content
+
+struct ProgressShareContent: ShareableContent {
+    let progress: LeagueProgress
+    let tripCount: Int
+    let username: String?
+
+    var cardType: ShareCardType { .stadiumProgress }
+
+    @MainActor
+    func render(theme: ShareTheme) async throws -> UIImage {
+        let mapGenerator = ShareMapSnapshotGenerator()
+        let mapSnapshot = await mapGenerator.generateProgressMap(
+            visited: progress.stadiumsVisited,
+            remaining: progress.stadiumsRemaining,
+            theme: theme
+        )
+
+        let cardView = ProgressCardView(
+            progress: progress,
+            tripCount: tripCount,
+            username: username,
+            theme: theme,
+            mapSnapshot: mapSnapshot
+        )
+
+        let renderer = ImageRenderer(content: cardView)
+        renderer.scale = 3.0
+
+        guard let image = renderer.uiImage else {
+            throw ShareError.renderingFailed
+        }
+
+        return image
+    }
+}
+
+// MARK: - Progress Card View
+
+private struct ProgressCardView: View {
+    let progress: LeagueProgress
+    let tripCount: Int
+    let username: String?
+    let theme: ShareTheme
+    let mapSnapshot: UIImage?
+
+    var body: some View {
+        ZStack {
+            ShareCardBackground(theme: theme)
+
+            VStack(spacing: 40) {
+                ShareCardHeader(
+                    title: "\(progress.sport.displayName) Stadium Quest",
+                    sport: progress.sport,
+                    theme: theme
+                )
+
+                Spacer()
+
+                // Progress ring
+                ShareProgressRing(
+                    current: progress.visitedStadiums,
+                    total: progress.totalStadiums,
+                    theme: theme
+                )
+
+                Text("\(Int(progress.completionPercentage))% Complete")
+                    .font(.system(size: 28, weight: .medium))
+                    .foregroundStyle(theme.secondaryTextColor)
+
+                // Stats row
+                ShareStatsRow(
+                    stats: [
+                        (value: "\(progress.visitedStadiums)", label: "visited"),
+                        (value: "\(progress.totalStadiums - progress.visitedStadiums)", label: "remain"),
+                        (value: "\(tripCount)", label: "trips")
+                    ],
+                    theme: theme
+                )
+
+                // Map
+                if let snapshot = mapSnapshot {
+                    Image(uiImage: snapshot)
+                        .resizable()
+                        .aspectRatio(contentMode: .fit)
+                        .frame(maxWidth: 960)
+                        .clipShape(RoundedRectangle(cornerRadius: 20))
+                        .overlay {
+                            RoundedRectangle(cornerRadius: 20)
+                                .stroke(theme.accentColor.opacity(0.3), lineWidth: 2)
+                        }
+                }
+
+                Spacer()
+
+                ShareCardFooter(theme: theme, username: username)
+            }
+            .padding(ShareCardDimensions.padding)
+        }
+        .frame(
+            width: ShareCardDimensions.cardSize.width,
+            height: ShareCardDimensions.cardSize.height
+        )
+    }
+}