feat(engine): add resources, events, and GamePlugin event routing

Introduces the plumbing layer for Phase 3: GameStateResource wraps
solitaire_core::GameState, DragState tracks in-progress drags, and
SyncStatusResource holds runtime sync status. GamePlugin routes
Draw/Move/Undo/NewGame request events into GameState and emits
StateChangedEvent and GameWonEvent for downstream systems.

Also adds the Phase 3 implementation plan under docs/superpowers/plans/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/Cargo.toml

@@ -9,3 +9,4 @@ bevy_egui       = { workspace = true }
 bevy_kira_audio = { workspace = true }
 solitaire_core  = { workspace = true }
 solitaire_data  = { workspace = true }
+chrono          = { workspace = true }