feat(rules): add game-specific metadata attachment and unify match metadata initialization

Added AttachGameMetadata to GameRules interface

Implemented metadata setup for Battleship (phase + readiness flags)

Implemented no-op metadata hook for TicTacToe

Moved generic phase/ready metadata out of MatchInit

Added game/mode metadata to match state

Fixed json:"metadata" tag in MatchState

plugins/games/rules.go

@@ -21,6 +21,8 @@ type GameRules interface {
     // Assign symbols/colors/pieces at start.
     AssignPlayerSymbols(players []*structs.Player)
 
+    // Attach Game Metadata
+    AttachGameMetadata(state *structs.MatchState)
     // Apply a move.
     // Returns: (changed, gameOver, winnerIndex)
     ApplyMove(