feat: add gemini-3-flash to fast models list (#6497)

Co-authored-by: qio <[email protected]>

packages/opencode/src/provider/provider.ts

@@ -1018,6 +1018,7 @@ export namespace Provider {
         "claude-haiku-4.5",
         "3-5-haiku",
         "3.5-haiku",
+        "gemini-3-flash",
         "gemini-2.5-flash",
         "gpt-5-nano",
       ]