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/http/server.go

@@ -1,18 +1,18 @@
-// Package api provides the HTTP server and routing for the banking service.
+// Package api provides the HTTP server and routing for the service.
 package api
 
 import (
 	"context"
 	"net/http"
 
-	"github.com/FernandoJVideira/simple_bank/internal/auth"
-	"github.com/FernandoJVideira/simple_bank/internal/config"
-	"github.com/FernandoJVideira/simple_bank/internal/domain/role"
-	"github.com/FernandoJVideira/simple_bank/internal/service"
-	"github.com/FernandoJVideira/simple_bank/internal/worker"
+	"github.com/FernandoJVideira/api_tmpl/internal/auth"
+	"github.com/FernandoJVideira/api_tmpl/internal/config"
+	"github.com/FernandoJVideira/api_tmpl/internal/domain/role"
+	"github.com/FernandoJVideira/api_tmpl/internal/service"
+	"github.com/FernandoJVideira/api_tmpl/internal/worker"
 	"github.com/rs/zerolog/log"
 
-	db "github.com/FernandoJVideira/simple_bank/internal/db/sqlc"
+	db "github.com/FernandoJVideira/api_tmpl/internal/db/sqlc"
 	"github.com/gin-gonic/gin"
 
 	"github.com/gin-contrib/cors"
@@ -20,7 +20,7 @@ import (
 	ginSwagger "github.com/swaggo/gin-swagger"
 )
 
-// Server serves HTTP requests for our banking service.
+// Server serves HTTP requests for our service.
 type Server struct {
 	config         config.Config
 	store          db.Store