feat: 更新小模型为Gemini 3 Flash并新增高精度与图像模型选项

- 更新小模型为Gemini 3 Flash，并新增Gemini 3 Pro高精度和图像模型选项。

opencode.jsonc

@@ -3,7 +3,7 @@
   "autoupdate": "notify",
   "theme": "tokyonight",
   "model": "gateway/claude-sonnet-4-5",
-  "small_model": "gateway/gemini-3-flash-preview",
+  "small_model": "gateway/gemini-3-flash",
   "plugin": [
     "@tarquinen/opencode-dcp@latest",
     "@franlol/opencode-md-table-formatter@latest"
@@ -46,10 +46,13 @@
         "claude-haiku-4-5": {
           "name": "Claude Haiku 4.5"
         },
-        "gemini-3-pro-preview": {
-          "name": "Gemini 3 Pro"
+        "gemini-3-pro-high": {
+          "name": "Gemini 3 Pro (High)"
         },
-        "gemini-3-flash-preview": {
+        "gemini-3-pro-image": {
+          "name": "Gemini 3 Pro (Image)"
+        },
+        "gemini-3-flash": {
           "name": "Gemini 3 Flash"
         },
         "gpt-5.2": {