feat: avatar upload via presigned PUT URL flow

- Go scraper: add PresignAvatarUploadURL/PresignAvatarURL/DeleteAvatar to
  Store interface, implement on HybridStore+MinioClient, register
  GET /api/presign/avatar-upload/{userId} and /api/presign/avatar/{userId}
- SvelteKit: replace direct AWS S3 SDK in minio.ts with presign calls to
  the Go scraper; rewrite avatar +server.ts (POST=presign, PATCH=record key)
- iOS: rewrite uploadAvatar() as 3-step presigned PUT flow; refactor
  chip components into shared ChipButton in CommonViews.swift

scraper/internal/storage/hybrid.go

@@ -316,6 +316,18 @@ func (h *HybridStore) PresignAudio(ctx context.Context, key string, expires time
 	return h.minio.PresignAudio(ctx, key, expires)
 }
 
+func (h *HybridStore) PresignAvatarUpload(ctx context.Context, userID, ext string) (string, string, error) {
+	return h.minio.PresignAvatarUploadURL(ctx, userID, ext)
+}
+
+func (h *HybridStore) PresignAvatarURL(ctx context.Context, userID string) (string, bool, error) {
+	return h.minio.PresignAvatarURL(ctx, userID)
+}
+
+func (h *HybridStore) DeleteAvatar(ctx context.Context, userID string) error {
+	return h.minio.DeleteAvatar(ctx, userID)
+}
+
 // ─── Browse page snapshots ────────────────────────────────────────────────────
 
 func (h *HybridStore) SaveBrowsePage(ctx context.Context, key, html string) error {

scraper/internal/storage/minio.go

@@ -362,6 +362,22 @@ func (m *MinioClient) PutAvatar(ctx context.Context, userID, ext string, data []
 	return nil
 }
 
+// PresignAvatarUploadURL returns a presigned PUT URL for uploading an avatar image
+// directly to MinIO from the client. Signed with the public endpoint so iOS/browser
+// can PUT bytes straight to MinIO without routing through the server.
+// ext should be "jpg", "png", or "webp". Expires in 15 minutes.
+func (m *MinioClient) PresignAvatarUploadURL(ctx context.Context, userID, ext string) (string, string, error) {
+	if m.cfg.BucketAvatars == "" {
+		return "", "", fmt.Errorf("minio: avatars bucket not configured")
+	}
+	key := avatarKey(userID, ext)
+	u, err := m.pub.PresignedPutObject(ctx, m.cfg.BucketAvatars, key, 15*time.Minute)
+	if err != nil {
+		return "", "", fmt.Errorf("minio: presign avatar upload %s: %w", key, err)
+	}
+	return u.String(), key, nil
+}
+
 // PresignAvatarURL returns a presigned GET URL for a user avatar.
 // Returns ("", false, nil) when no avatar exists for the given userID.
 func (m *MinioClient) PresignAvatarURL(ctx context.Context, userID string) (string, bool, error) {

scraper/internal/storage/store.go

@@ -160,6 +160,17 @@ type Store interface {
 	// PresignAudio returns a presigned GET URL for an audio object.
 	PresignAudio(ctx context.Context, key string, expires time.Duration) (string, error)
 
+	// PresignAvatarUpload returns a short-lived presigned PUT URL for uploading
+	// an avatar image directly to MinIO, and the object key that will be stored.
+	// ext should be "jpg", "png", or "webp".
+	PresignAvatarUpload(ctx context.Context, userID, ext string) (uploadURL, key string, err error)
+
+	// PresignAvatarURL returns a presigned GET URL for a user's avatar, or ("", false, nil) if none.
+	PresignAvatarURL(ctx context.Context, userID string) (string, bool, error)
+
+	// DeleteAvatar removes all avatar objects for a user (all extensions).
+	DeleteAvatar(ctx context.Context, userID string) error
+
 	// ── Browse page snapshots (MinIO) ──────────────────────────────────────
 
 	// SaveBrowsePage stores a SingleFile HTML snapshot for the given cache key.