chore(ops): align default service port to 4000 across runtime and docs

Reduce deployment and smoke-test drift by using one default port across Puma, docker smoke probes, and OpenAPI examples.

Decision: standardize on 4000 to match current container/devcontainer wiring and README guidance.

Tradeoff: environments implicitly relying on legacy 3000 defaults must now set PORT explicitly, which is safer than silent mismatch.

Author: gildesmarais

config/puma.rb

@@ -15,5 +15,5 @@
   log_requests false
 end
 
-port        ENV.fetch('PORT', 3000)
+port        ENV.fetch('PORT', 4000)
 environment ENV.fetch('RACK_ENV', 'development')

docs/api/v1/openapi.yaml

@@ -15,7 +15,7 @@ info:
 servers:
   - url: https://html2rss-web.example.com/api/v1
     description: Production server
-  - url: http://localhost:3000/api/v1
+  - url: http://localhost:4000/api/v1
     description: Development server
 
 security:

spec/smoke/docker_spec.rb

@@ -5,7 +5,7 @@
 require 'uri'
 
 RSpec.describe 'Dockerized API smoke test', :docker do # rubocop:disable RSpec/DescribeClass
-  let(:base_url) { ENV.fetch('SMOKE_BASE_URL', 'http://127.0.0.1:3000') }
+  let(:base_url) { ENV.fetch('SMOKE_BASE_URL', 'http://127.0.0.1:4000') }
   let(:health_token) { ENV.fetch('SMOKE_HEALTH_TOKEN', 'health-check-token-xyz789') }
   let(:feed_token) { ENV.fetch('SMOKE_API_TOKEN', 'allow-any-urls-abcd-4321') }