fix(config): Improve config manager flexibility & test mocks

Refactored `config-manager.js` to handle different execution contexts (CLI vs. MCP) and fixed related Jest tests.

- Modified `readConfig` and `writeConfig` to accept an optional `explicitRoot` parameter, allowing explicit path specification (e.g., from MCP) while retaining automatic project root finding for CLI usage.

- Updated getter/setter functions (`getMainProvider`, `setMainModel`, etc.) to accept and propagate the `explicitRoot`.

- Resolved Jest testing issues for dynamic imports by using `jest.unstable_mockModule` for `fs` and `chalk` dependencies *before* the dynamic `import()`.

- Corrected console error assertions in tests to match exact logged messages.

- Updated `.cursor/rules/tests.mdc` with guidelines for `jest.unstable_mockModule` and precise console assertions.

.taskmasterconfig

@@ -0,0 +1,12 @@
+{
+  "models": {
+    "main": {
+      "provider": "openai",
+      "modelId": "gpt-4o"
+    },
+    "research": {
+      "provider": "google",
+      "modelId": "gemini-1.5-pro-latest"
+    }
+  }
+}