feat(ollama): add OCO_OLLAMA_THINK config to control thinking mode

Adds support for passing the `think` param to Ollama's /api/chat endpoint,
allowing users to disable reasoning blocks on models like qwen3.5 via
`oco config set OCO_OLLAMA_THINK=false`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/unit/ollama.test.ts

@@ -0,0 +1,64 @@
+import { OllamaEngine } from '../../src/engine/ollama';
+
+describe('OllamaEngine', () => {
+  it('sends think=false when configured', async () => {
+    const engine = new OllamaEngine({
+      apiKey: 'ollama',
+      model: 'qwen3.5:2b',
+      maxTokensOutput: 500,
+      maxTokensInput: 4096,
+      ollamaThink: false
+    });
+
+    const post = jest.fn().mockResolvedValue({
+      data: {
+        message: {
+          content: 'feat: add support for ollama think config'
+        }
+      }
+    });
+
+    engine.client = { post } as any;
+
+    await engine.generateCommitMessage([
+      { role: 'user', content: 'diff --git a/file b/file' }
+    ]);
+
+    expect(post).toHaveBeenCalledWith(
+      'http://localhost:11434/api/chat',
+      expect.objectContaining({
+        think: false
+      })
+    );
+  });
+
+  it('omits think when not configured', async () => {
+    const engine = new OllamaEngine({
+      apiKey: 'ollama',
+      model: 'qwen3.5:2b',
+      maxTokensOutput: 500,
+      maxTokensInput: 4096
+    });
+
+    const post = jest.fn().mockResolvedValue({
+      data: {
+        message: {
+          content: 'feat: add support for ollama think config'
+        }
+      }
+    });
+
+    engine.client = { post } as any;
+
+    await engine.generateCommitMessage([
+      { role: 'user', content: 'diff --git a/file b/file' }
+    ]);
+
+    expect(post).toHaveBeenCalledWith(
+      'http://localhost:11434/api/chat',
+      expect.not.objectContaining({
+        think: expect.anything()
+      })
+    );
+  });
+});