feat: add CrossRef DOI verification (Check 3b) Resolve each DOI via CrossRef API and compare returned metadata

Fix validation logic and formatting

Use Click callback for file validation

Change bibtex_file to option for consistency with other parameters

Remove redundant FileNotFoundError handler

Fix validation to allow default file when it doesn't exist yet

Make all hyperparameters optional with defaults

Make max_retries configurable via command-line argument

Fix author verification tracking to match "Could not verify metadata automatically" count

Add summary section for citations with unverified author lists

Add missing colon and improve comment clarity

Fix 403 error counting and reformat summary output

Add 403 error count to summary and manual verification reminder

Require complete author lists for 'and others' entries and add verbose logging

Improve author matching with fuzzy logic and update color coding for better UX

Improve verification heuristics and address code review feedback

Add core citation verification implementation