feat(battleship): add full placement/battle phases + metadata support + action-based moves

- Added Battleship Fleet definition (carrier, battleship, cruiser, submarine, destroyer)
- Implemented action-based MovePayload (`action: "place" | "shoot"`)
- Added placement and shot validation (ValidatePlacementMove, ValidateShotMove)
- Added ApplyPlacement and ApplyShot with correct ship placement + hit/miss logic
- Added pX_placed, pX_ready tracking and phase switching (placement → battle)
- Added Metadata field to MatchState (for phase/ready tracking)
- Updated MatchInit to initialize placement phase and readiness flags
- Updated MatchLoop to enforce turn order only during battle phase
- Added debug logging for state broadcasts
- Fixed protobuf dependency marking as indirect

plugins/structs/match_state.go

@@ -2,9 +2,10 @@ package structs
 
 // MatchState holds the full game session state.
 type MatchState struct {
-  Players  []*Player           `json:"players"`
-  Boards map[string]*Board     `json:"boards"`      // Multiple named boards:
-  Turn     int                 `json:"turn"`        // index in Players[]
-  Winner   int                 `json:"winner"`      // -1 = none, >=0 = winner index
-  GameOver bool                `json:"game_over"`   // true when the match ends
+  Players  []*Player              `json:"players"`
+  Boards   map[string]*Board      `json:"boards"`      // Multiple named boards:
+  Turn     int                    `json:"turn"`        // index in Players[]
+  Winner   int                    `json:"winner"`      // -1 = none, >=0 = winner index
+  GameOver bool                   `json:"game_over"`   // true when the match ends
+  Metadata map[string]interface{} `json:metadata`     // metadata
 }