feat(ui): replace loading indicators with Apple-style LoadingSpinner

- Add LoadingSpinner component with small/medium/large sizes using system gray color
- Add LoadingPlaceholder for skeleton loading states
- Add LoadingSheet for full-screen blocking overlays
- Replace ThemedSpinner/ThemedSpinnerCompact across all views
- Remove deprecated loading components from AnimatedComponents.swift
- Delete LoadingTextGenerator.swift
- Fix PhotoImportView layout to fill full width

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

SportsTimeTests/Loading/LoadingSheetTests.swift

@@ -0,0 +1,28 @@
+//
+//  LoadingSheetTests.swift
+//  SportsTimeTests
+//
+
+import Testing
+import SwiftUI
+@testable import SportsTime
+
+struct LoadingSheetTests {
+
+    @Test func sheetRequiresLabel() {
+        let sheet = LoadingSheet(label: "Planning trip")
+        #expect(sheet.label == "Planning trip")
+    }
+
+    @Test func sheetCanHaveOptionalDetail() {
+        let withDetail = LoadingSheet(label: "Exporting", detail: "Generating maps...")
+        let withoutDetail = LoadingSheet(label: "Loading")
+
+        #expect(withDetail.detail == "Generating maps...")
+        #expect(withoutDetail.detail == nil)
+    }
+
+    @Test func backgroundOpacityIsCorrect() {
+        #expect(LoadingSheet.backgroundOpacity == 0.5)
+    }
+}