refactor: adopt portigo infrastructure patterns

Add config package with build-tag-switched dev/prod environments,
structured logging via zerolog, Taskfile for dev workflow, golangci-lint
config, testutil package, and improved DB setup with proper SQLite
pragmas and cleanup. Rename sqlc output package from gen to repository.

Switch to allowlist .gitignore, Alpine+UPX+scratch Dockerfile, and
CI pipeline with test/lint gates before deploy.

db/repository/models.go

@@ -0,0 +1,54 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.30.0
+
+package repository
+
+import (
+	"database/sql"
+)
+
+type ChatMessage struct {
+	ID        int64
+	GameID    string
+	Nickname  string
+	Color     int64
+	Message   string
+	CreatedAt int64
+}
+
+type Game struct {
+	ID            string
+	Board         string
+	CurrentTurn   int64
+	Status        int64
+	WinnerUserID  sql.NullString
+	WinningCells  sql.NullString
+	CreatedAt     sql.NullTime
+	UpdatedAt     sql.NullTime
+	RematchGameID sql.NullString
+	GameType      string
+	GridWidth     sql.NullInt64
+	GridHeight    sql.NullInt64
+	MaxPlayers    int64
+	GameMode      int64
+	Score         int64
+	SnakeSpeed    int64
+}
+
+type GamePlayer struct {
+	GameID        string
+	UserID        sql.NullString
+	GuestPlayerID sql.NullString
+	Nickname      string
+	Color         int64
+	Slot          int64
+	CreatedAt     sql.NullTime
+}
+
+type User struct {
+	ID           string
+	Username     string
+	PasswordHash string
+	CreatedAt    sql.NullTime
+}