[Bug]: TermsAndConditionsUIParams.mainTextColor does not apply to all text elements in consent dialog

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Description of the bug

When using `GoogleMapsNavigator.showTermsAndConditionsDialog()` with custom `TermsAndConditionsUIParams`, the `**mainTextColor**` parameter does not apply to all text elements. Certain body text sections remain in a hardcoded color (black) rather than using the provided `mainTextColor`.

### Flutter version

3.38.7

### Package version

0.8.2

### Native SDK versions

- [x] I haven't changed the version of the native SDKs

### Flutter Doctor Output

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.38.7, on macOS 26.2 25C56 darwin-arm64, locale en-BG)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0-rc1)
[✓] Xcode - develop for iOS and macOS (Xcode 26.2)
[✓] Chrome - develop for the web
[✓] Connected device (3 available)
[✓] Network resources

• No issues found!

### Steps to reproduce

1. Create a Flutter app with google_navigation_flutter package
2. Configure dark-themed `TermsAndConditionsUIParams` (see code sample below)
3. Call `GoogleMapsNavigator.showTermsAndConditionsDialog()` with the params
4. Observe the consent dialog - some text is invisible (black on dark background)

### Expected vs Actual Behavior

### Expected Behavior
All body text in the terms and conditions dialog should use the `mainTextColor` (white in this example).

### Actual Behavior
Only some text elements use `mainTextColor`. The following sections remain black, making them invisible on a dark background:

- "How navigation data is used" section header and body
- "When you use [App] Ltd., Google collects..." paragraph
- "These updates to the map won't be associated..." paragraph
- "How driver reports and edits are used" section header and body

### Code Sample

```dart
final uiParams = TermsAndConditionsUIParams(
backgroundColor: Colors.black,
titleColor: Colors.white,
mainTextColor: Colors.white, // Should apply to all body text
acceptButtonTextColor: Colors.blue,
cancelButtonTextColor: Colors.grey,
);

await GoogleMapsNavigator.showTermsAndConditionsDialog(
'App Title',
'Company Name',
uiParams: uiParams,
);
```

### Additional Context

_No response_