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

proto/service_api_tmpl.proto

@@ -0,0 +1,66 @@
+syntax = "proto3";
+
+package pb;
+
+import "google/api/annotations.proto";
+import "rpc_create_user.proto";
+import "rpc_login_user.proto";
+import "rpc_update_user.proto";
+import "rpc_verify_email.proto";
+import "protoc-gen-openapiv2/options/annotations.proto";
+
+option go_package = "github.com/FernandoJVideira/api_tmpl/pb";
+
+option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_swagger) = {
+  info: {
+    title: "API Template"
+    version: "0.0.1"
+    contact: {
+      name: "fvideira"
+      url: "https://github.com/FernandoJVideira/api_tmpl"
+      email: "[email protected]"
+    };
+  };
+};
+
+service ApiTmpl {
+    rpc CreateUser (CreateUserRequest) returns (CreateUserResponse){
+        option (google.api.http) = {
+            post: "/v1/create_user"
+            body: "*"
+        };
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+              description: "Create a new user."
+              summary: "Create User"
+        };
+    }
+    rpc LoginUser (LoginUserRequest) returns (LoginUserResponse){
+        option (google.api.http) = {
+            post: "/v1/login_user"
+            body: "*"
+        };
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+              description: "Login an existing user."
+              summary: "Login User"
+        };
+    }
+    rpc VerifyEmail (VerifyEmailRequest) returns (VerifyEmailResponse){
+        option (google.api.http) = {
+            get: "/v1/verify_email"
+        };
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+              description: "Verify a user's email."
+              summary: "Verify Email"
+        };
+    }
+    rpc UpdateUser (UpdateUserRequest) returns (UpdateUserResponse){
+        option (google.api.http) = {
+            patch: "/v1/update_user"
+            body: "*"
+        };
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+              description: "Update an existing user."
+              summary: "Update User"
+        };
+    }
+}