fix(shared): honor absolute schema paths

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Summary

• resolve configured schema paths against the working directory while preserving absolute paths
• add a regression test that loads a model from an absolute repository path

Verification

• yarn workspace @cubejs-backend/shared unit --runTestsByPath test/FileRepository.test.ts --runInBand
• yarn workspace @cubejs-backend/shared tsc
• ESLint passed for both changed files (with linebreak-style disabled locally because Git for Windows checked the sparse worktree out as CRLF)

Fixes #10746