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

Dockerfile

@@ -5,7 +5,7 @@ WORKDIR /api
 
 COPY . .
 
-RUN go build -o main main.go
+RUN go build -o main ./cmd/api
 
 
 #Run stage
@@ -16,9 +16,10 @@ COPY --from=builder /api/main .
 COPY api.env .
 COPY start.sh .
 COPY wait-for.sh .
-COPY db/migrations ./db/migrations
+COPY cmd/db/migrations ./cmd/db/migrations
 
 EXPOSE 8080
+EXPOSE 9090
 
 CMD [ "/api/main" ]
 ENTRYPOINT [ "/api/start.sh" ]