always use engine (#1525)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Always route Dyad Pro through the Dyad engine (no gateway), simplify
logging/flags, and remove DYAD_GATEWAY usage and staging gateway script.
> 
> - **Engine/Model client (`src/ipc/utils/get_model_client.ts`)**:
> - Always use `createDyadEngine` when Dyad Pro is enabled; remove
gateway fallback and `DYAD_GATEWAY_URL` usage.
> - Simplify logs to engine-only; drop conditional gateway/engine
logging.
> - Always set `isEngineEnabled: true`; pass `{ files }` to the provider
unconditionally; strip `:free` from model names.
> - **Scripts (`package.json`)**:
>   - Remove `staging:gateway` script.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
5fdbbb703c47de4623ceeb82e6678ace34dc268e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

e2e-tests/gateway.spec.ts

@@ -1,19 +0,0 @@
-import { testSkipIfWindows } from "./helpers/test_helper";
-
-testSkipIfWindows("claude 4 sonnet", async ({ po }) => {
-  await po.setUpDyadPro();
-  // Disable the pro modes so it routes to gateway.
-  const proModesDialog = await po.openProModesDialog({
-    location: "home-chat-input-container",
-  });
-  await proModesDialog.toggleTurboEdits();
-  await proModesDialog.setSmartContextMode("off");
-  await proModesDialog.close();
-
-  await po.selectModel({ provider: "Anthropic", model: "Claude 4 Sonnet" });
-
-  await po.sendPrompt("[dump] tc=gateway-simple");
-
-  await po.snapshotServerDump("request");
-  await po.snapshotMessages({ replaceDumpPath: true });
-});