Replace thinking with native Gemini thinking summaries (#400)

This uses Gemini's native [thinking
summaries](https://cloud.google.com/vertex-ai/generative-ai/docs/thinking#thought-summaries)
which were recently added to the API.

Why? The grafted thinking would sometimes cause weird issues where the
model, especially Gemini 2.5 Flash, got confused and put dyad tags like
`<dyad-write>` inside the `<think>` tags.

This also improves the UX because you can see the native thoughts rather
than having the Gemini response load for a while without any feedback.

I tried adding Anthropic extended thinking, however it requires temp to
be set at 1, which isn't ideal for Dyad's use case where we need precise
syntax following.

e2e-tests/helpers/test_helper.ts

@@ -139,10 +139,14 @@ export class PageObject {
     });
   }
 
-  async openProModesDialog(): Promise<ProModesDialog> {
+  async openProModesDialog({
+    location = "chat-input-container",
+  }: {
+    location?: "chat-input-container" | "home-chat-input-container";
+  } = {}): Promise<ProModesDialog> {
     const proButton = this.page
       // Assumes you're on the chat page.
-      .getByTestId("chat-input-container")
+      .getByTestId(location)
       .getByRole("button", { name: "Pro", exact: true });
     await proButton.click();
     return new ProModesDialog(this.page, async () => {
@@ -396,7 +400,7 @@ export class PageObject {
   async selectModel({ provider, model }: { provider: string; model: string }) {
     await this.page.getByRole("button", { name: "Model: Auto" }).click();
     await this.page.getByText(provider).click();
-    await this.page.getByText(model).click();
+    await this.page.getByText(model, { exact: true }).click();
   }
 
   async selectTestModel() {