fix: remove duplicate 1280x800@60 viewport entry

The viewport '1280x800@60' was added twice:
- Once in commit 899caee (SDK v0.29.0 update)
- Again in commit 4d9565b (feat: add 1280x800 viewport support #97)

This resulted in 8 items in getAvailableViewports() while the test
expected 7 items, causing test failures.

Also removes the duplicate assertion in the test file.

Co-authored-by: mason <mason@onkernel.com>

Author: cursoragent

cmd/browsers.go

@@ -127,7 +127,6 @@ func getAvailableViewports() []string {
 		"1280x800@60",
 		"1024x768@60",
 		"1200x800@60",
-		"1280x800@60",
 	}
 }
 

cmd/browsers_test.go

@@ -1153,7 +1153,6 @@ func TestGetAvailableViewports_ReturnsExpectedOptions(t *testing.T) {
 	assert.Contains(t, viewports, "1440x900@25")
 	assert.Contains(t, viewports, "1280x800@60")
 	assert.Contains(t, viewports, "1200x800@60")
-	assert.Contains(t, viewports, "1280x800@60")
 	assert.Contains(t, viewports, "1024x768@60")
 }