feat: persist chat messages to SQLite

Chat messages were ephemeral — lost on page refresh or late join.
Add a chat_messages table and load the last 50 messages on connect
so players see conversation history.

db/persister.go

@@ -3,10 +3,12 @@ package db
 import (
 	"context"
 	"database/sql"
+	"slices"
 
 	"github.com/ryanhamamura/c4/db/gen"
 	"github.com/ryanhamamura/c4/game"
 	"github.com/ryanhamamura/c4/snake"
+	"github.com/ryanhamamura/c4/ui"
 )
 
 type GamePersister struct {
@@ -286,3 +288,40 @@ func (p *SnakePersister) DeleteSnakeGame(id string) error {
 	ctx := context.Background()
 	return p.queries.DeleteSnakeGame(ctx, id)
 }
+
+type ChatPersister struct {
+	queries *gen.Queries
+}
+
+func NewChatPersister(q *gen.Queries) *ChatPersister {
+	return &ChatPersister{queries: q}
+}
+
+func (p *ChatPersister) SaveChatMessage(gameID string, msg ui.C4ChatMessage) error {
+	return p.queries.CreateChatMessage(context.Background(), gen.CreateChatMessageParams{
+		GameID:    gameID,
+		Nickname:  msg.Nickname,
+		Color:     int64(msg.Color),
+		Message:   msg.Message,
+		CreatedAt: msg.Time,
+	})
+}
+
+func (p *ChatPersister) LoadChatMessages(gameID string) ([]ui.C4ChatMessage, error) {
+	rows, err := p.queries.GetChatMessages(context.Background(), gameID)
+	if err != nil {
+		return nil, err
+	}
+	msgs := make([]ui.C4ChatMessage, len(rows))
+	for i, r := range rows {
+		msgs[i] = ui.C4ChatMessage{
+			Nickname: r.Nickname,
+			Color:    int(r.Color),
+			Message:  r.Message,
+			Time:     r.CreatedAt,
+		}
+	}
+	// Query returns newest-first; reverse to oldest-first for display
+	slices.Reverse(msgs)
+	return msgs, nil
+}