Adds a 19th achievement: "Cinephile — Watch a saved replay all the
way through." Unlocks the first time ReplayPlaybackState transitions
Playing → Completed (i.e. the move list runs out without the player
pressing Stop). Discoverability nudge for the replay feature itself.
The achievement uses the existing event-driven unlock pattern
(condition closure returns false; an unlock system fires
AchievementUnlockedEvent on the right state transition) rather than
the standard condition-evaluation path, mirroring how other
non-stat-driven achievements work.
The unlock system distinguishes natural completion from Stop-button
abort by watching for the specific Playing → Completed transition;
Stop transitions Playing → Inactive directly without going through
Completed, so it doesn't fire the achievement. Already-unlocked
state is checked via AchievementsResource so the achievement can't
double-fire on subsequent replays.
README's "18 Achievements" → "19 Achievements". ARCHITECTURE.md §11
gains a Cinephile entry alongside the existing 18.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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