Fix: Slot reservation only after successful email validation

- Move email validation before slot reservation in backend
- Remove duplicate frontend email validation
- Slots are no longer blocked by failed booking attempts
- Clean up unused email error UI components
- Ensure slots remain available if email validation fails

src/server/routes/rpc.ts

@@ -21,10 +21,7 @@ rpcApp.all("/*", async (c) => {
   } catch (error) {
     console.error("RPC Handler error:", error);
     
-    // Preserve the original error message if it's a known error
-    const errorMessage = error instanceof Error ? error.message : "Internal server error";
-    const statusCode = error instanceof Error && error.message.includes("bereits eine Buchung") ? 400 : 500;
-    
-    return c.json({ error: errorMessage }, statusCode);
+    // Let oRPC handle errors properly
+    throw error;
   }
 });