Game Deduplication on Import

[nloding]

Problem

No option to skip duplicate games during PGN import. Would require content hashing or move comparison.

Proposed Solution

Add --dedupe flag to import command:

scidtopgn import games.pgn -o mydb --dedupe

Implementation Options

1. Hash-based: Hash player names + move sequence
2. Full comparison: Compare all game data (slower but more accurate)
3. Index lookup: Check if same players played on same date

Priority

Low - optimization for large imports