fix: low-contrast secondary text color in global theme token

## Description

The LESS variable `text-color-secondary` is set to `#c0c0ca`, which has poor contrast on light backgrounds (commonly white in Ant Design layouts). Because this token is used globally, secondary labels, helper text, and metadata can become hard to read for low-vision users and may fail WCAG AA contrast requirements.

**Severity**: `medium`
**File**: `amoro-web/vite.config.ts`

## Expected Behavior

The code should handle this case properly to avoid unexpected errors or degraded quality.

Start by inspecting amoro-web/vite.config.ts and locating the LESS variable text-color-secondary. Check the replacement color against the stated light-background contrast requirement and verify that the global secondary labels, helper text, and metadata remain readable and meet WCAG AA contrast expectations.

Written by the indexing model from the issue text.