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, 1 insertions, 1 deletions

diff --git a/backend/api/auth_middleware.go b/backend/api/auth_middleware.go
index d721f1d..0b0dfc8 100644
--- a/backend/api/auth_middleware.go
+++ b/backend/api/auth_middleware.go
@@ -12,7 +12,7 @@ import (
 type sessionIDContextKey struct{}
 type userContextKey struct{}
 
-func SessionCookieMiddleware(q *db.Queries) echo.MiddlewareFunc {
+func SessionCookieMiddleware(q db.Querier) echo.MiddlewareFunc {
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
 			cookie, err := c.Cookie("albatross_session")