feat: improve first-time contributor developer experience

bin/validate_configs (new):
- Single Ruby process validates all configs via Html2rss::Config.validate,
  replacing 48 separate bundle exec invocations (~2 min → seconds)
- Prints per-file ok/FAIL status with inline error details on failure
- Friendly error when the installed gem predates the validate API

make validate:
- Now calls bin/validate_configs instead of xargs + bundle exec loop

bin/setup:
- Removed set -vx (noisy shell tracing unhelpful for contributors)
- Installs prettier via npm so make lint works immediately after setup
- Checks for yamllint with install instructions if missing
- Prints a next-steps command reference on completion

.vscode/extensions.json (new):
- Recommends redhat.vscode-yaml so VS Code prompts to install the
  extension needed to surface the schema modeline hints

https://claude.ai/code/session_01MYdMDpKySqfU1E3qgdikoe

Author: claude

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+  "recommendations": [
+    "redhat.vscode-yaml"
+  ]
+}

Makefile

@@ -6,7 +6,7 @@ lint:
 	npx prettier --check lib/**/*.yml .github/**/*.yml README.md
 
 validate:
-	find lib/html2rss/configs -name '*.yml' -print0 | xargs -0 -n1 bundle exec html2rss validate
+	bundle exec ruby bin/validate_configs
 
 schema:
 	mkdir -p schema

bin/setup

@@ -1,8 +1,33 @@
 #!/usr/bin/env bash
 set -euo pipefail
 IFS=$'\n\t'
-set -vx
 
+echo "==> Installing Ruby dependencies..."
 bundle install
 
-# Do any other automated setup that you need to do here
+echo
+echo "==> Installing Node dependencies (required for make lint)..."
+npm install --no-fund --no-audit --no-save prettier
+
+echo
+echo "==> Checking system tools..."
+if command -v yamllint &>/dev/null; then
+  echo "    yamllint: ok ($(yamllint --version))"
+else
+  echo "    yamllint: not found"
+  echo "    Install with one of:"
+  echo "      brew install yamllint"
+  echo "      pip install yamllint"
+fi
+
+echo
+echo "==> Setup complete. Common commands:"
+echo
+echo "    make              # lint + validate + test"
+echo "    make lint         # yamllint, rubocop, prettier"
+echo "    make validate     # validate all configs against the html2rss schema"
+echo "    make test         # run rspec"
+echo
+echo "    make test-config CONFIG=github.com/releases.yml   # test a single config"
+echo "    make test-domain DOMAIN=github.com                # test all configs for a domain"
+echo "    make schema                                        # write schema locally (optional)"

bin/validate_configs

@@ -0,0 +1,38 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'bundler/setup'
+require 'html2rss'
+require 'yaml'
+
+unless Html2rss::Config.respond_to?(:validate)
+  warn 'Error: installed html2rss gem does not support Config.validate.'
+  warn 'Run: bundle update html2rss'
+  exit 1
+end
+
+files = Dir['lib/html2rss/configs/**/*.yml'].sort
+failed = []
+
+files.each do |file|
+  config = YAML.safe_load_file(file, symbolize_names: true)
+  result = Html2rss::Config.validate(config)
+
+  if result.success?
+    puts "ok   #{file}"
+  else
+    puts "FAIL #{file}"
+    result.errors.to_h.each do |key, messages|
+      Array(messages).each { |msg| warn "       #{key}: #{msg}" }
+    end
+    failed << file
+  end
+end
+
+puts
+if failed.empty?
+  puts "#{files.size} configs validated successfully."
+else
+  warn "#{failed.size}/#{files.size} configs failed validation."
+  exit 1
+end