fix(core): remediate validation feedback loss and access control silent errors

[envsecure]

Description

This PR provides a comprehensive fix for several issues in the KeystoneJS core, including those that led to CI failures in previous attempts (PR #9837).

Key Improvements:

1. Validation Feedback Preservation:
   • Fixed an issue where field-level validation messages were lost if a list-level validation hook threw an exception.
   • Field validation messages are now prioritized and preserved even during list-level hook crashes, providing better feedback to users.
2. Access Control Robustness:
   • Resolved a silent error in checkUniqueItemExists where database errors (connection timeouts, etc.) were being swallowed.
   • These errors are now correctly rethrown, while preserving the "item may not exist" logic for actual access denied cases.
3. Build & Type Stability:
   • Simplified the complex generic type signatures in hooks.ts that were causing Preconstruct/Rollup build failures (MISSING_EXPORT).
   • Standardized export patterns and import styles to ensure consistent behavior across bundling tools.
4. API Consistency:
   • Updated internal error tags and documentation from validateInput to validate to align with the current public API names.

Changes

• Modified packages/core/src/lib/core/hooks.ts
• Modified packages/core/src/lib/core/access-control.ts
• Modified packages/core/src/types/config/hooks.ts
• Added two changesets for the respective fixes.

Verification

• The logic has been audited to ensure no regressions in hook execution order or field-level hook filtering.
• The build-breaking complex generics have been refactored into simpler, more robust patterns.