fix: don't show prebuild workspaces as tasks (#19572)

Fixes #19570

**Before:**

<img width="2776" height="1274" alt="image"
src="https://github.com/user-attachments/assets/bd260dbf-0868-4e4a-9997-b2fd3c99f33c"
/>

**After:**

<img width="1624" height="970" alt="Screenshot 2025-08-27 at 09 11 31"
src="https://github.com/user-attachments/assets/c85489d8-031c-4cbe-8298-6fee04e30b1f"
/>

**Things to notice:**
- There is a task without a prompt at the end, it should not happen
anymore
- There is no test for this because we mock the API function and the fix
was inside of it. It is a temp solution, the API should be ready to be
used by the FE soon

Author: BrunoQuaresma

site/src/api/api.ts

@@ -2702,14 +2702,18 @@ class ExperimentalApiMethods {
 			queryExpressions.push(`owner:${filter.username}`);
 		}
 
-		const workspaces = await API.getWorkspaces({
+		const res = await API.getWorkspaces({
 			q: queryExpressions.join(" "),
 		});
+		// Exclude prebuild workspaces as they are not user-facing.
+		const workspaces = res.workspaces.filter(
+			(workspace) => !workspace.is_prebuild,
+		);
 		const prompts = await API.experimental.getAITasksPrompts(
-			workspaces.workspaces.map((workspace) => workspace.latest_build.id),
+			workspaces.map((workspace) => workspace.latest_build.id),
 		);
 
-		return workspaces.workspaces.map((workspace) => ({
+		return workspaces.map((workspace) => ({
 			workspace,
 			prompt: prompts.prompts[workspace.latest_build.id],
 		}));