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/db/mock/store.go

@@ -1,9 +1,9 @@
 // Code generated by MockGen. DO NOT EDIT.
-// Source: github.com/FernandoJVideira/simple_bank/internal/db/sqlc (interfaces: Store)
+// Source: github.com/FernandoJVideira/api_tmpl/internal/db/sqlc (interfaces: Store)
 //
 // Generated by this command:
 //
-//	mockgen --package mockdb --destination internal/db/mock/store.go github.com/FernandoJVideira/simple_bank/internal/db/sqlc Store
+//	mockgen --package mockdb --destination internal/db/mock/store.go github.com/FernandoJVideira/api_tmpl/internal/db/sqlc Store
 //
 
 // Package mockdb is a generated GoMock package.
@@ -13,7 +13,7 @@ import (
 	context "context"
 	reflect "reflect"
 
-	db "github.com/FernandoJVideira/simple_bank/internal/db/sqlc"
+	db "github.com/FernandoJVideira/api_tmpl/internal/db/sqlc"
 	uuid "github.com/google/uuid"
 	gomock "go.uber.org/mock/gomock"
 )

internal/db/sqlc/main_test.go

@@ -6,7 +6,7 @@ import (
 	"os"
 	"testing"
 
-	"github.com/FernandoJVideira/simple_bank/internal/config"
+	"github.com/FernandoJVideira/api_tmpl/internal/config"
 	"github.com/jackc/pgx/v5/pgxpool"
 	_ "github.com/jackc/pgx/v5/stdlib"
 )

internal/db/sqlc/user_test.go

@@ -5,8 +5,8 @@ import (
 	"testing"
 	"time"
 
-	"github.com/FernandoJVideira/simple_bank/internal/security"
-	"github.com/FernandoJVideira/simple_bank/pkg/testutil"
+	"github.com/FernandoJVideira/api_tmpl/internal/security"
+	"github.com/FernandoJVideira/api_tmpl/pkg/testutil"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/stretchr/testify/require"
 )