feat: update Claude model to Opus 4.6 and enhance adaptive thinking support

- Changed model identifier from `claude-opus-4-5-20251101` to `claude-opus-4-6` across various files, including documentation and code references.
- Updated the SDK to support adaptive thinking for Opus 4.6, allowing the model to determine its own reasoning depth.
- Enhanced the thinking level options to include 'adaptive' and adjusted related components to reflect this change.
- Updated tests to ensure compatibility with the new model and its features.

These changes improve the model's capabilities and user experience by leveraging adaptive reasoning.

libs/model-resolver/tests/resolver.test.ts

@@ -484,12 +484,12 @@ describe('model-resolver', () => {
 
       it('should handle full Claude model string in entry', () => {
         const entry: PhaseModelEntry = {
-          model: 'claude-opus-4-5-20251101',
+          model: 'claude-opus-4-6',
           thinkingLevel: 'high',
         };
         const result = resolvePhaseModel(entry);
 
-        expect(result.model).toBe('claude-opus-4-5-20251101');
+        expect(result.model).toBe('claude-opus-4-6');
         expect(result.thinkingLevel).toBe('high');
       });
     });