Fix repository scans not respecting cache policies in DAK selection

[Copilot]

Repository scans in the DAK selection page were triggering unnecessary rescans every time an authenticated user browsed the page, bypassing the 24-hour cache policy.

Root Cause

The issue was caused by cascading useCallback dependencies in DAKSelection.js:

1. getMockRepositories and simulateEnhancedScanning were dependencies of the fetchRepositories useCallback
2. These helper functions depended on effectiveProfile
3. When the profile changed (even to the same value), the helper functions were recreated
4. This caused fetchRepositories to be recreated, triggering the useEffect that calls it
5. The cache check was bypassed, leading to unnecessary GitHub API calls

Solution

• Used useRef to store the current profile, allowing helper functions to access it without depending on it
• Made helper functions stable with empty or minimal dependencies
• Removed helper functions from fetchRepositories dependencies
• Added comprehensive documentation explaining the fix and ESLint disable rationale

Before vs After

Before: Every profile state change → helper functions recreated → fetchRepositories recreated → useEffect triggered → cache bypassed → unnecessary API call

After: Only actual profile/action changes → fetchRepositories recreated → cache properly checked → API call only when cache is stale/missing

Testing

• Application builds successfully without linting errors
• Existing repository cache integration tests pass
• Manual verification shows cache policies are now respected

This ensures the 24-hour cache policy works as intended, preventing unnecessary GitHub API calls and improving performance for authenticated users browsing DAK repositories.

Fixes #456.

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