refactor: move contextWindowSize to ContentGeneratorConfig

- Add contextWindowSize field to ContentGeneratorConfig interface
- Update tokenLimit function to accept contentGeneratorConfig parameter
- Implement priority logic: user config > auto-detection
- Update chatCompressionService to use new API via getContentGeneratorConfig()
- Add contextWindowSize to MODEL_GENERATION_CONFIG_FIELDS for config resolution
- Add contextWindowSize to CLI settings schema (model.generationConfig)
- Update UI components (Footer, ContextUsageDisplay) to use new config API
- Fix test mocks to include getContentGeneratorConfig method

This refactor avoids modifying 71+ test files by moving the config
to the generator level instead of the Config class level.

Modified files:
- packages/core/src/core/contentGenerator.ts
- packages/core/src/core/tokenLimits.ts
- packages/core/src/services/chatCompressionService.ts
- packages/core/src/services/chatCompressionService.test.ts
- packages/core/src/models/constants.ts
- packages/cli/src/config/settingsSchema.ts
- packages/cli/src/ui/components/ContextUsageDisplay.tsx
- packages/cli/src/ui/components/Footer.tsx

packages/cli/src/config/settingsSchema.ts

@@ -690,6 +690,18 @@ const SETTINGS_SCHEMA = {
               { value: 'openapi_30', label: 'OpenAPI 3.0 Strict' },
             ],
           },
+          contextWindowSize: {
+            type: 'number',
+            label: 'Context Window Size',
+            category: 'Generation Configuration',
+            requiresRestart: false,
+            default: -1,
+            description:
+              'Override the automatic context window size detection. Set to -1 to use automatic detection based on the model. Set to a positive number to use a custom context window size.',
+            parentKey: 'generationConfig',
+            childKey: 'contextWindowSize',
+            showInDialog: true,
+          },
         },
       },
     },