Fix SPA routing: serve index.html for non-file paths

Replace bare http.FileServer with an SPA-aware handler that tries to
serve the requested static file and falls back to index.html when
the path doesn't match a real file. This lets React Router handle
client-side routes like /schedules on page reload.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/server/server.go

@@ -94,8 +94,25 @@ func New(db *sql.DB, jwtSecret string, staticDir string) http.Handler {
 		})
 	})
 
-	// Serve static React app for all other routes
-	r.Handle("/*", http.FileServer(http.Dir(staticDir)))
+	// Serve static React app for all other routes, with SPA fallback
+	r.Handle("/*", spaHandler(staticDir))
 
 	return r
 }
+
+// spaHandler serves static files from dir, falling back to index.html for
+// paths that don't match a file on disk (so client-side routing works).
+func spaHandler(dir string) http.HandlerFunc {
+	fs := http.Dir(dir)
+	fileServer := http.FileServer(fs)
+	return func(w http.ResponseWriter, r *http.Request) {
+		// Try to open the requested path as a static file.
+		if f, err := fs.Open(r.URL.Path); err == nil {
+			f.Close()
+			fileServer.ServeHTTP(w, r)
+			return
+		}
+		// Not a real file — serve index.html and let React Router handle it.
+		http.ServeFile(w, r, dir+"/index.html")
+	}
+}