Update all mentions of gemini-1.5 models with gemini-2.5 (#571)

This commit updates all occurrences of `gemini-1.5` model names to their `gemini-2.5` counterparts, and removes any versioning suffixes.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: google-labs-jules[bot]

ai/devdocs-link-preview/Vertex.js

@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 const VERTEX_AI_LOCATION = scriptPropertyWithDefault('project_location', 'us-central1');
-const MODEL_ID = scriptPropertyWithDefault('model_id', 'gemini-1.5-flash-preview-0514');
+const MODEL_ID = scriptPropertyWithDefault('model_id', 'gemini-2.5-flash');
 const SERVICE_ACCOUNT_KEY = scriptPropertyWithDefault('service_account_key');
 
 /**

ai/gmail-sentiment-analysis/Vertex.gs

@@ -16,7 +16,7 @@ limitations under the License.
 
 const PROJECT_ID = [ADD YOUR GCP PROJECT ID HERE];
 const VERTEX_AI_LOCATION = 'europe-west2';
-const MODEL_ID = 'gemini-1.5-pro-002';
+const MODEL_ID = 'gemini-2.5-pro';
 const SERVICE_ACCOUNT_KEY = PropertiesService.getScriptProperties().getProperty('service_account_key');
 
 /**