Grow Steam detection coverage: curate more known games / explore dynamic detection

[dyoung522]

Deferred to a future cycle (user decision 2026-08-02): the embedded known-games list has 13 entries, so game detect finds few games in large libraries. Two directions, not mutually exclusive:

1. Curate more entries — each needs verified App ID, mod path, and source mapping (per-game research; candidates should come from actual user demand).
2. Dynamic detection — e.g. any Steam game with a NexusMods domain is plausibly moddable; the hard part staying curated is the per-game mod path (a generic fallback + loud "verify mod_path" warning could bridge it).

Interim: the ~/.config/lmm/steam-games.yaml user override already allows extending detection without a rebuild (docs shipping separately).

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