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.

testutil/sessions.go

@@ -0,0 +1,31 @@
+package testutil
+
+import (
+	"database/sql"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/alexedwards/scs/sqlite3store"
+	"github.com/alexedwards/scs/v2"
+)
+
+// NewTestSessionManager creates an SCS session manager backed by the
+// provided SQLite database. The background cleanup goroutine is stopped
+// automatically when the test finishes.
+func NewTestSessionManager(t *testing.T, db *sql.DB) *scs.SessionManager {
+	t.Helper()
+
+	store := sqlite3store.New(db)
+	t.Cleanup(func() { store.StopCleanup() })
+
+	sm := scs.New()
+	sm.Store = store
+	sm.Lifetime = 30 * 24 * time.Hour
+	sm.Cookie.Path = "/"
+	sm.Cookie.HttpOnly = true
+	sm.Cookie.Secure = false
+	sm.Cookie.SameSite = http.SameSiteLaxMode
+
+	return sm
+}