chore: rename simple_bank to api_tmpl and clean up for template use

Rename the module, proto service, and all identifiers from simple_bank/
SimpleBank to api_tmpl/ApiTmpl, and regenerate the gRPC/gateway/swagger/
mock code accordingly.

- Scrub real secrets (SMTP password, auth token secret) from api.env/
  api_test.env, untrack them, and add api.env.example/api_test.env.example
- Remove committed build artifacts (tmp/main, tmp/build-errors.log,
  dbml-error.log) and gitignore them going forward
- Fix Dockerfile paths (build target, migrations copy) that referenced a
  stale project layout
- Rewrite README to match the actual cmd/ + internal/ structure and add a
  "using this as a template" section

internal/handlers/grpc/server.go

@@ -1,24 +1,24 @@
-// Package gapi implements the gRPC server for the Simple Bank application.
+// Package gapi implements the gRPC server for the API Template application.
 package gapi
 
 import (
-	"github.com/FernandoJVideira/simple_bank/internal/auth"
-	"github.com/FernandoJVideira/simple_bank/internal/config"
-	db "github.com/FernandoJVideira/simple_bank/internal/db/sqlc"
-	"github.com/FernandoJVideira/simple_bank/internal/service"
-	"github.com/FernandoJVideira/simple_bank/internal/worker"
-	"github.com/FernandoJVideira/simple_bank/pb"
+	"github.com/FernandoJVideira/api_tmpl/internal/auth"
+	"github.com/FernandoJVideira/api_tmpl/internal/config"
+	db "github.com/FernandoJVideira/api_tmpl/internal/db/sqlc"
+	"github.com/FernandoJVideira/api_tmpl/internal/service"
+	"github.com/FernandoJVideira/api_tmpl/internal/worker"
+	"github.com/FernandoJVideira/api_tmpl/pb"
 )
 
-// Server serves gRPC requests for our banking service.
+// Server serves gRPC requests for our service.
 type Server struct {
-	pb.UnimplementedSimpleBankServer // Embedding for forward compatibility
-	config                           config.Config
-	store                            db.Store
-	tokenMaker                       auth.Maker
-	taskDistributor                  worker.TaskDistributor
-	userService                      service.UserService
-	authService                      service.AuthService
+	pb.UnimplementedApiTmplServer // Embedding for forward compatibility
+	config                        config.Config
+	store                         db.Store
+	tokenMaker                    auth.Maker
+	taskDistributor               worker.TaskDistributor
+	userService                   service.UserService
+	authService                   service.AuthService
 }
 
 // NewServer creates a new gRPC server instance.