feat: add markets support

[gil93]

Summary

Adds Markets support to Shopkeeper buckets and updates ignore rules so required fixtures are tracked. Improves docs and tests accordingly.

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What’s Changed

.gitignore

• Keep ignoring .shopkeeper globally, but unignore src/utilities/fixtures/.shopkeeper/ so repo fixtures are tracked.

README / Docs

• Show config/markets.json in the example tree.
• Document ignore patterns relevant to markets fixtures for theme projects.

Patterns & Flags

• getSettingsPatterns() now returns: ['config/settings_data.json', 'config/markets.json', 'templates/**/*.json', 'sections/*.json']
• CLI_SETTINGS_FLAGS includes config/markets.json so --only flags cover markets.
• getSettingsFolders() left unchanged (no locales added here).

Bucket Scaffolding

• Ensure bucket scaffolding recognizes config/markets.json where applicable (no locales folder created in this PR).

Tests

• Extend tests to assert presence of config/markets.json in pulls/flags.

Fixtures

• Add empty fixture files for:
  • src/utilities/fixtures/.shopkeeper/production/config/markets.json
  • src/utilities/fixtures/theme/config/markets.json

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Why

• Themes commonly rely on Markets config; this should be part of bucket operations.
• We need repo-scoped .shopkeeper fixtures tracked for tests/docs, while still ignoring other .shopkeeper paths.

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Behavior / Compatibility

• Backward compatible for existing buckets (recognizes config/markets.json if present).

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Testing

• Ran unit tests (vitest --run).
• Manual verification via local file: install that --only flags include config/markets.json.

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Split from #177