Phase 3: Foto-Upload + Mindeststrecken-Warnung

- APIClient.uploadFile: multipart POST mit Bearer-Token, generischer
  field/filename/mime
- ImageResize: längste Kante max 2048px, JPEG q=0.8 — iPhone-Fotos sonst
  5-10MB pro Stück
- FinishWalkSheet:
  - PhotosPicker (iOS 16+, kein NSPhotoLibraryUsageDescription nötig)
  - Thumbnail-Strip der gewählten Fotos
  - Sequentieller Upload nach POST /api/routes, Toolbar zeigt "N/M"
  - Bei < 50m: orangene Warnung "Sehr kurze Tour — du kannst trotzdem speichern"
  - Save-Button blockt korrekt während Upload, Verwerfen auch

BanYaroGo/Support/ImageResize.swift

@@ -0,0 +1,31 @@
+import UIKit
+
+enum ImageResize {
+    /// Resizes a JPEG/PNG so its longest edge is at most `maxDimension`,
+    /// then re-encodes as JPEG with the given quality. Returns the original
+    /// data if it can't be decoded.
+    static func resizedJPEG(
+        from data: Data,
+        maxDimension: CGFloat = 2048,
+        quality: CGFloat = 0.8
+    ) -> Data {
+        guard let image = UIImage(data: data) else { return data }
+        let longest = max(image.size.width, image.size.height)
+        guard longest > maxDimension else {
+            // already small enough — just re-encode to JPEG
+            return image.jpegData(compressionQuality: quality) ?? data
+        }
+        let scale = maxDimension / longest
+        let target = CGSize(width: image.size.width * scale, height: image.size.height * scale)
+        let renderer = UIGraphicsImageRenderer(size: target, format: {
+            let f = UIGraphicsImageRendererFormat.default()
+            f.scale = 1
+            f.opaque = true
+            return f
+        }())
+        let resized = renderer.image { _ in
+            image.draw(in: CGRect(origin: .zero, size: target))
+        }
+        return resized.jpegData(compressionQuality: quality) ?? data
+    }
+}