Remember which games the user removed

[Vasanthdev2004]

Closes #61.

gsg remove hogwarts-legacy --purge deleted the game and its backups. The next rescan added it straight back. Same for GTA V Enhanced. Observed on a real install: 11 tracked games, then 9, then 11 again, within two hours.

Why

Auto-add skipped a game only when detect_launcher said a launcher owned it. Epic writes a manifest per installed game, so a title Epic is not currently showing classifies as other and becomes eligible all over again. Removing recorded nothing — there was no memory that the user had said no.

The periodic rescan added in 0.8.1 did not cause this. It made an existing hole visible on a timer rather than once per reboot.

This matters more than tidiness: --purge is destructive and irreversible. Watching the game reappear teaches people the command does not work, and re-running it burns another delete cycle on data recreated in between.

The fix

declined_game_ids in config. gsg remove appends, auto_add_skip_reason consults it first — an explicit decision by the user outranks anything gsg worked out for itself — and an explicit gsg add clears it, so the list can never become a trap that silently ignores a direct request.

The scan reports what it is skipping and why:

Not tracking 2 game(s) you removed: Hogwarts Legacy, Roblox.
'gsg add "<title>"' to track one again.

A list that suppresses games invisibly is its own trap, and this is how someone works out why a game they installed is not appearing.

Both gsg remove and gsg remove --purge record. They should not differ by accident, and "stop tracking this" is what remove means. gsg pause already exists for "stop watching for now" and deliberately records nothing — there is a test pinning that, because the two verbs drifting apart is the obvious way this goes wrong later.

Verification

End to end through the real commands: remove writes the id, a second remove does not duplicate it, add clears it, pause leaves it alone.

Five mutations, all caught:

remove stops recording       caught
predicate ignores the list   caught
add stops clearing           caught
discovery stops passing it   caught
pause starts declining       caught

336 tests, ruff and mypy clean.