Per-user podcasts, file uploads, RSS images, Docker support

- Each user owns a podcast: podcast title/author/image on users table
- Episodes scoped by user_id with context-based auth
- Audio file upload replaces URL linking, served from /uploads/
- Podcast and per-episode images with itunes:image in RSS
- RSS per-user via ?user=N, dashboard shows user-specific feed URL
- Settings form for title + author + image per user
- Docker multi-stage build (golang:1.25-alpine / alpine:3.21)
- Removed PODSTALK_TITLE/AUTHOR env vars

handler/settings.go

@@ -19,32 +19,55 @@ func (h *SettingsHandler) ServeSettings(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
+	userID := UserIDFromContext(r)
+	user, err := h.Store.GetUser(userID)
+	if err != nil {
+		http.Redirect(w, r, "/", http.StatusSeeOther)
+		return
+	}
+
 	if err := r.ParseMultipartForm(10 << 20); err != nil {
 		http.Redirect(w, r, "/?error=file+too+large", http.StatusSeeOther)
 		return
 	}
 
 	title := r.FormValue("podcast_title")
-	if title != "" {
-		h.Store.SetSetting("podcast_title", title)
+	if title == "" {
+		title = user.PodcastTitle
 	}
 
+	author := r.FormValue("podcast_author")
+	if author == "" {
+		author = user.PodcastAuthor
+	}
+
+	image := user.PodcastImage
+
 	// Handle podcast image upload
 	file, header, err := r.FormFile("podcast_image")
 	if err == nil {
 		defer file.Close()
 
+		// Remove old image
+		if image != "" {
+			os.Remove(filepath.Join(h.UploadDir, image))
+		}
+
 		catDir := filepath.Join(h.UploadDir, "images")
 		os.MkdirAll(catDir, 0755)
 
 		ext := filepath.Ext(header.Filename)
+		if ext == "" {
+			ext = ".png"
+		}
 		dst, err := os.Create(filepath.Join(catDir, "podcast"+ext))
 		if err == nil {
 			defer dst.Close()
 			dst.ReadFrom(file)
-			h.Store.SetSetting("podcast_image", "images/podcast"+ext)
+			image = "images/podcast" + ext
 		}
 	}
 
+	h.Store.UpdateUserPodcast(userID, title, image, author)
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }