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

api_test.env.example

@@ -0,0 +1,45 @@
+PKG_NAME=github.com/FernandoJVideira/api_tmpl
+
+PROJ_NAME=api_tmpl
+
+SERVICE_NAME="API Template"
+
+# Server Configuration
+HTTP_SERVER_ADDR=:8080
+GRPC_SERVER_ADDR=:9090
+EXTERNAL_URL=localhost:8080
+FRONTEND_URL=http://localhost:5173
+ENVIRONMENT=development
+ALLOWED_ORIGINS=https://*,http://* # TODO: Change to the actual allowed origins on production
+
+# Database Configuration
+DB_ADDR=postgres://postgres:postgres@localhost:5432/api_tmpl?sslmode=disable
+DB_USERNAME=postgres
+DB_PASSWORD=postgres
+DB_MAX_OPEN_CONNS=30
+DB_MAX_IDLE_CONNS=30
+DB_MAX_IDLE_TIME=15m
+MIGRATIONS_URL=file://cmd/db/migrations
+
+# Redis Configuration
+REDIS_ADDR=localhost:6379
+REDIS_PASSWORD=
+REDIS_DB=0
+
+# Authentication
+AUTH_TOKEN_SECRET=changeme-replace-with-a-random-secret-at-least-32-chars
+AUTH_TOKEN_MIN_KEY_SIZE=32
+AUTH_TOKEN_EXP=15m
+REFRESH_TOKEN_EXP=168h
+AUTH_TOKEN_ISS=api_tmpl
+AUTH_TOKEN_AUD=api_tmpl
+
+# Email Configuration
+EMAIL_FROM=[email protected]
+EMAIL_FROM_NAME=API Template
+EMAIL_SMTP_PASSWORD=changeme-smtp-app-password
+
+# Rate Limiter
+RATE_LIMITER_REQS_COUNT=20
+RATE_LIMITER_TIME_FRAME=1m
+RATE_LIMITER_ENABLED=true