feat: support VertexAI provider (#153)

* support: vertexai

fix

fix

set default for vertexai

added comment

fix

fix

* create schema

* fix README.md

* fix order

* added pupularity

* set tools if tools is exists

restore commentout

* fix comment

* set summarizer model

README.md

@@ -74,6 +74,8 @@ You can configure OpenCode using environment variables:
 | `ANTHROPIC_API_KEY`        | For Claude models                                      |
 | `OPENAI_API_KEY`           | For OpenAI models                                      |
 | `GEMINI_API_KEY`           | For Google Gemini models                               |
+| `VERTEXAI_PROJECT`         | For Google Cloud VertexAI (Gemini)                     |
+| `VERTEXAI_LOCATION`        | For Google Cloud VertexAI (Gemini)                     |
 | `GROQ_API_KEY`             | For Groq models                                        |
 | `AWS_ACCESS_KEY_ID`        | For AWS Bedrock (Claude)                               |
 | `AWS_SECRET_ACCESS_KEY`    | For AWS Bedrock (Claude)                               |
@@ -189,6 +191,11 @@ OpenCode supports a variety of AI models from different providers:
 - O3 family (o3, o3-mini)
 - O4 Mini
 
+### Google Cloud VertexAI
+
+- Gemini 2.5
+- Gemini 2.5 Flash
+ 
 ## Usage
 
 ```bash