feat: opt-in export of detected card info to files

[leiteszeke]

Fork-internal PR (base up/06-remote-decklist) — kept out of upstream for now because it depends on the unpublished backend half. Here for change tracking until the draw2 backend side is ready; will be opened upstream then.

Summary

Adds an opt-in "Export detected card info to files" toggle (Draw 2 settings → Feature flags, off by default): when on, the plugin points each backend detector at a stable per-user folder and the backend writes the currently-detected cards there, so you can surface them anywhere — an OBS Text source the streamer reads on stream, bots, or HTML/browser overlays. With the flag off, nothing is set and the backend behaves exactly as upstream.

Changes

• src/feature_flags.h — FEATURE_CARD_INFO key.
• src/plugin-path.h / src/plugin-main.cpp — get_state_path() helper (per-user plugin_config/draw2-plugin/state dir, created on demand), mirroring get_decklists_path().
• src/SettingsDialog.{cpp,hpp} — in the Feature flags tab: an Export detected card info to files checkbox (QSettings feature_card_info), plus a Download full card database for offline use checkbox (QSettings feature_card_info_db, on by default) that controls whether the backend uses its local offline DB or resolves lazily per card.
• src/DrawDock.cpp — when card info is on, each backend process is launched with DRAW2_CARD_INFO_DIR (= the state dir), DRAW2_CARD_INFO_LANG (QSettings card_info_lang, default en) and DRAW2_CARD_INFO_DB (1/0 from the toggle). When off, no environment is set. With debug logging on (FEATURE_DEBUG, from feat: opt-in debug logging (plugin-side) HichTala/draw2-plugin#29) the dock log shows the resolved output dir, language and full_db.
• README + all translations (es/fr/jp/pt-br) document the toggle and the file contract.

File contract (written by the backend, per player N)

• current_pN.json — cards currently on screen: { updated_at, channel, cards: [ { id, name, type, attribute, race, atk, def, desc } ] } (rich fields from YGOPRODeck; missing fields omitted).
• events_pN.jsonl — append-only, one JSON per line: { ts, event: "appeared" | "disappeared", card: { … } }.
• current_card_pN.txt — plain text, names on screen (newline-separated); point an OBS Text source at it (Read from file).

Opt-in / default behaviour

Off by default: with it off, no env var is set and the backend writes nothing — identical to upstream.

Backend dependency

This is the plugin half: it only sets the env vars pointing at the output folder. The backend reads DRAW2_CARD_INFO_DIR / DRAW2_CARD_INFO_LANG and writes the files (the draw2 backend change). With a backend that doesn't support it, the toggle is a no-op (no files written), no crash.

How it was tested

• Universal plugin build succeeds (cmake --preset macos).