fix: improve Gemini compatibility by adding configurable schema converter

This commit addresses issue #1186 by introducing a configurable schema compliance
mechanism for tool definitions sent to LLMs.

Key changes:
1.  **New Configuration**: Added `model.generationConfig.schemaCompliance` setting (defaults to 'auto', optional 'openapi_30').
2.  **Schema Converter**: Implemented `toOpenAPI30` converter in `packages/core` to strictly downgrade modern JSON Schema to OpenAPI 3.0.3 (required for Gemini API), handling:
    -   Nullable types (`["string", "null"]` -> `nullable: true`)
    -   Numeric exclusive limits
    -   Const to Enum conversion
    -   Removal of tuples and invalid keywords (``, `dependencies`, etc.)
3.  **Tests**: Added comprehensive unit tests for the schema converter and updated pipeline tests.

Fixes #1186

packages/cli/src/config/settingsSchema.ts

@@ -628,6 +628,22 @@ const SETTINGS_SCHEMA = {
             childKey: 'disableCacheControl',
             showInDialog: true,
           },
+          schemaCompliance: {
+            type: 'enum',
+            label: 'Tool Schema Compliance',
+            category: 'Generation Configuration',
+            requiresRestart: false,
+            default: 'auto',
+            description:
+              'The compliance mode for tool schemas sent to the model. Use "openapi_30" for strict OpenAPI 3.0 compatibility (e.g., for Gemini).',
+            parentKey: 'generationConfig',
+            childKey: 'schemaCompliance',
+            showInDialog: true,
+            options: [
+              { value: 'auto', label: 'Auto (Default)' },
+              { value: 'openapi_30', label: 'OpenAPI 3.0 Strict' },
+            ],
+          },
         },
       },
     },