refactor(backend): introduce DI interfaces for testability

Replace concrete *db.Queries and *pgxpool.Pool dependencies with
db.Querier and db.TxManager interfaces across all handlers, game hub,
and auth. This enables unit testing with mocks.

- Enable sqlc emit_interface to generate Querier interface
- Add TxManager abstraction to encapsulate transactions
- Convert auth package-level functions to Authenticator struct
- Add TaskQueueInterface/TaskWorkerInterface for game.Hub
- Add initial unit tests for game logic and API handlers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/backend/main.go b/backend/main.go
index 01ed784..f936cf4 100644
--- a/backend/main.go
+++ b/backend/main.go
@@ -16,6 +16,7 @@ import (
 
 	"albatross-2026-backend/admin"
 	"albatross-2026-backend/api"
+	"albatross-2026-backend/auth"
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
 	"albatross-2026-backend/game"
@@ -61,6 +62,8 @@ func main() {
 	defer connPool.Close()
 
 	queries := db.New(connPool)
+	txm := db.NewTxManager(connPool, queries)
+	authenticator := auth.NewAuthenticator(queries, txm)
 
 	e := echo.New()
 	e.Renderer = admin.NewRenderer()
@@ -91,7 +94,7 @@ func main() {
 	taskQueue := taskqueue.NewQueue("task-db:6379")
 	workerServer := taskqueue.NewWorkerServer("task-db:6379")
 
-	gameHub := game.NewGameHub(queries, connPool, taskQueue, workerServer)
+	gameHub := game.NewGameHub(queries, txm, taskQueue, workerServer)
 
 	loginRL := ratelimit.NewIPRateLimiter(rate.Every(time.Minute/5), 5)
 
@@ -99,10 +102,10 @@ func main() {
 	apiGroup.Use(ratelimit.LoginRateLimitMiddleware(loginRL))
 	apiGroup.Use(api.SessionCookieMiddleware(queries))
 	apiGroup.Use(oapimiddleware.OapiRequestValidator(openAPISpec))
-	apiHandler := api.NewHandler(queries, connPool, gameHub, conf)
+	apiHandler := api.NewHandler(queries, txm, gameHub, authenticator, conf)
 	api.RegisterHandlers(apiGroup, api.NewStrictHandler(apiHandler, nil))
 
-	adminHandler := admin.NewHandler(queries, connPool, conf)
+	adminHandler := admin.NewHandler(queries, txm, conf)
 	adminGroup := e.Group(conf.BasePath + "admin")
 	adminGroup.Use(api.SessionCookieMiddleware(queries))
 	adminHandler.RegisterHandlers(adminGroup)