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/server/handlers_audio.go

@@ -649,3 +649,64 @@ func (s *Server) handlePresignVoiceSample(w http.ResponseWriter, r *http.Request
 	w.Header().Set("Content-Type", "application/json")
 	_ = json.NewEncoder(w).Encode(map[string]string{"url": url})
 }
+
+// handlePresignAvatarUpload handles GET /api/presign/avatar-upload/{userId}.
+// Returns a short-lived presigned PUT URL for uploading an avatar image directly
+// to MinIO, along with the object key to record in PocketBase after the upload.
+// Query param: ext — image extension (jpg, png, webp). Defaults to "jpg".
+func (s *Server) handlePresignAvatarUpload(w http.ResponseWriter, r *http.Request) {
+	userID := r.PathValue("userId")
+	if userID == "" {
+		http.Error(w, `{"error":"missing userId"}`, http.StatusBadRequest)
+		return
+	}
+
+	ext := r.URL.Query().Get("ext")
+	switch ext {
+	case "jpg", "jpeg":
+		ext = "jpg"
+	case "png":
+		ext = "png"
+	case "webp":
+		ext = "webp"
+	default:
+		ext = "jpg"
+	}
+
+	uploadURL, key, err := s.store.PresignAvatarUpload(r.Context(), userID, ext)
+	if err != nil {
+		s.log.Error("presign avatar upload failed", "userId", userID, "err", err)
+		http.Error(w, `{"error":"presign failed"}`, http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(map[string]string{
+		"upload_url": uploadURL,
+		"key":        key,
+	})
+}
+
+// handlePresignAvatar handles GET /api/presign/avatar/{userId}.
+// Returns a presigned GET URL for a user's existing avatar, or 404 if none.
+func (s *Server) handlePresignAvatar(w http.ResponseWriter, r *http.Request) {
+	userID := r.PathValue("userId")
+	if userID == "" {
+		http.Error(w, `{"error":"missing userId"}`, http.StatusBadRequest)
+		return
+	}
+
+	url, found, err := s.store.PresignAvatarURL(r.Context(), userID)
+	if err != nil {
+		s.log.Error("presign avatar failed", "userId", userID, "err", err)
+		http.Error(w, `{"error":"presign failed"}`, http.StatusInternalServerError)
+		return
+	}
+	if !found {
+		http.NotFound(w, r)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(map[string]string{"url": url})
+}

scraper/internal/server/server.go

@@ -165,6 +165,8 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	mux.HandleFunc("GET /api/presign/chapter/{slug}/{n}", s.handlePresignChapter)
 	mux.HandleFunc("GET /api/presign/audio/{slug}/{n}", s.handlePresignAudio)
 	mux.HandleFunc("GET /api/presign/voice-sample/{voice}", s.handlePresignVoiceSample)
+	mux.HandleFunc("GET /api/presign/avatar-upload/{userId}", s.handlePresignAvatarUpload)
+	mux.HandleFunc("GET /api/presign/avatar/{userId}", s.handlePresignAvatar)
 	// Plain-text chapter content (used server-side for audio generation)
 	mux.HandleFunc("GET /api/chapter-text/{slug}/{n}", s.handleChapterText)
 	// Voices list (proxied from Kokoro)