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/LoadingPlaceholderTests.swift

@@ -0,0 +1,37 @@
+//
+//  LoadingPlaceholderTests.swift
+//  SportsTimeTests
+//
+
+import Testing
+import SwiftUI
+@testable import SportsTime
+
+struct LoadingPlaceholderTests {
+
+    @Test func rectangleHasCorrectDimensions() {
+        let rect = LoadingPlaceholder.rectangle(width: 100, height: 20)
+        #expect(rect.width == 100)
+        #expect(rect.height == 20)
+    }
+
+    @Test func circleHasCorrectDiameter() {
+        let circle = LoadingPlaceholder.circle(diameter: 40)
+        #expect(circle.diameter == 40)
+    }
+
+    @Test func capsuleHasCorrectDimensions() {
+        let capsule = LoadingPlaceholder.capsule(width: 80, height: 24)
+        #expect(capsule.width == 80)
+        #expect(capsule.height == 24)
+    }
+
+    @Test func animationCycleDurationIsCorrect() {
+        #expect(LoadingPlaceholder.animationDuration == 1.2)
+    }
+
+    @Test func opacityRangeIsSubtle() {
+        #expect(LoadingPlaceholder.minOpacity == 0.3)
+        #expect(LoadingPlaceholder.maxOpacity == 0.5)
+    }
+}