zed: add prompt_cache_key capability field to model entries

internal/adapters/zed/zed.go

@@ -124,6 +124,7 @@ func zedLanguageModels(p *canonical.Profile) map[string]any {
 					"tools":               true,
 					"images":              false,
 					"parallel_tool_calls": false,
+					"prompt_cache_key":    false,
 				},
 			}
 			if m.Alias != "" {

internal/adapters/zed/zed_test.go

@@ -152,6 +152,7 @@ func TestZedRenderEmitsLanguageModelsOpenAICompatible(t *testing.T) {
 	caps, ok := m0["capabilities"].(map[string]any)
 	require.True(t, ok, "model must have capabilities")
 	assert.Equal(t, true, caps["tools"])
+	assert.Equal(t, false, caps["prompt_cache_key"])
 }
 
 func TestZedImport(t *testing.T) {