WIP: Add multiplayer Snake game

N-player (2-8) real-time Snake game alongside Connect 4.
Lobby has tabs to switch between games. Players join via
invite link with 10-second countdown. Game loop runs at
tick-based intervals with NATS pub/sub for state sync.

Keyboard input not yet working (Datastar keydown binding
issue still under investigation).

snake/types.go

@@ -0,0 +1,148 @@
+package snake
+
+import (
+	"encoding/json"
+	"time"
+)
+
+type Direction int
+
+const (
+	DirUp Direction = iota
+	DirDown
+	DirLeft
+	DirRight
+)
+
+// Opposite returns true if a and b are 180-degree reversals.
+func (d Direction) Opposite(other Direction) bool {
+	switch d {
+	case DirUp:
+		return other == DirDown
+	case DirDown:
+		return other == DirUp
+	case DirLeft:
+		return other == DirRight
+	case DirRight:
+		return other == DirLeft
+	}
+	return false
+}
+
+type Point struct {
+	X int `json:"x"`
+	Y int `json:"y"`
+}
+
+type Snake struct {
+	Body    []Point   `json:"body"`
+	Dir     Direction `json:"dir"`
+	Alive   bool      `json:"alive"`
+	Growing bool      `json:"growing"`
+	Color   int       `json:"color"` // 1-8
+}
+
+type GameState struct {
+	Width  int      `json:"width"`
+	Height int      `json:"height"`
+	Snakes []*Snake `json:"snakes"`
+	Food   []Point  `json:"food"`
+}
+
+func (gs *GameState) ToJSON() string {
+	data, _ := json.Marshal(gs)
+	return string(data)
+}
+
+func GameStateFromJSON(data string) (*GameState, error) {
+	var gs GameState
+	if err := json.Unmarshal([]byte(data), &gs); err != nil {
+		return nil, err
+	}
+	return &gs, nil
+}
+
+type Status int
+
+const (
+	StatusWaitingForPlayers Status = iota
+	StatusCountdown
+	StatusInProgress
+	StatusFinished
+)
+
+type PlayerID string
+
+type Player struct {
+	ID       PlayerID
+	UserID   *string
+	Nickname string
+	Slot     int // 0-7
+}
+
+type SnakeGame struct {
+	ID            string
+	State         *GameState
+	Players       []*Player // up to 8
+	Status        Status
+	Winner        *Player   // nil if draw
+	CountdownEnd  time.Time // when countdown reaches 0
+	RematchGameID *string
+}
+
+func (sg *SnakeGame) IsFinished() bool {
+	return sg.Status == StatusFinished
+}
+
+func (sg *SnakeGame) PlayerCount() int {
+	count := 0
+	for _, p := range sg.Players {
+		if p != nil {
+			count++
+		}
+	}
+	return count
+}
+
+// Grid presets
+type GridPreset struct {
+	Name   string
+	Width  int
+	Height int
+}
+
+var GridPresets = []GridPreset{
+	{Name: "Small", Width: 20, Height: 20},
+	{Name: "Medium", Width: 30, Height: 20},
+	{Name: "Large", Width: 40, Height: 20},
+}
+
+// snapshot returns a shallow copy of the game safe for reading outside the lock.
+// Slices and pointers are shared but the top-level struct is copied.
+func (sg *SnakeGame) snapshot() *SnakeGame {
+	cp := *sg
+	if sg.State != nil {
+		stateCp := *sg.State
+		// Copy slices so the caller's iteration is safe
+		stateCp.Snakes = make([]*Snake, len(sg.State.Snakes))
+		copy(stateCp.Snakes, sg.State.Snakes)
+		stateCp.Food = make([]Point, len(sg.State.Food))
+		copy(stateCp.Food, sg.State.Food)
+		cp.State = &stateCp
+	}
+	cp.Players = make([]*Player, len(sg.Players))
+	copy(cp.Players, sg.Players)
+	return &cp
+}
+
+// Snake colors (hex values for CSS)
+var SnakeColors = []string{
+	"#00b894", // 1: Green
+	"#e17055", // 2: Orange
+	"#0984e3", // 3: Blue
+	"#6c5ce7", // 4: Purple
+	"#fd79a8", // 5: Pink
+	"#00cec9", // 6: Cyan
+	"#d63031", // 7: Red
+	"#fdcb6e", // 8: Yellow
+}