Slug-based RSS URLs and success flash messages

- Add podcast_slug to users with global uniqueness check
- RSS available at /rss/{slug} (path-based) with legacy ?slug= fallback
- Slug field in dashboard settings with validation (lowercase, hyphens)
- JS flash messages for success/error after form submissions
- Remove unused imports

handler/episode.go

@@ -43,6 +43,7 @@ func (h *EpisodeHandler) ServeDashboard(w http.ResponseWriter, r *http.Request)
 	h.Tpl.Render(w, "dashboard", map[string]any{
 		"Episodes":      episodes,
 		"PodcastTitle":  title,
+		"PodcastSlug":   user.PodcastSlug,
 		"PodcastImage":  user.PodcastImage,
 		"PodcastAuthor": user.PodcastAuthor,
 		"BaseURL":       h.BaseURL,
@@ -105,7 +106,7 @@ func (h *EpisodeHandler) ServeNew(w http.ResponseWriter, r *http.Request) {
 			})
 			return
 		}
-		http.Redirect(w, r, "/", http.StatusSeeOther)
+		http.Redirect(w, r, "/?success=episode+created", http.StatusSeeOther)
 	}
 }
 
@@ -181,7 +182,7 @@ func (h *EpisodeHandler) ServeEdit(w http.ResponseWriter, r *http.Request) {
 			http.Error(w, "update failed", http.StatusInternalServerError)
 			return
 		}
-		http.Redirect(w, r, "/", http.StatusSeeOther)
+		http.Redirect(w, r, "/?success=episode+updated", http.StatusSeeOther)
 	}
 }
 
@@ -208,7 +209,7 @@ func (h *EpisodeHandler) ServeDelete(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "delete failed", http.StatusInternalServerError)
 		return
 	}
-	http.Redirect(w, r, "/", http.StatusSeeOther)
+	http.Redirect(w, r, "/?success=episode+deleted", http.StatusSeeOther)
 }
 
 func (h *EpisodeHandler) ServeUpload(w http.ResponseWriter, r *http.Request) {