chore: release 3.6.18

[PHKenny]

Summary

• Added Poi and PoiInput models to the map module
• Added mapLayerId, mapLayer, pois, and poisIds fields to Locator model
• Added poisIds and mapLayerId fields to LocatorInput and MapLayerInput
• Updated CHANGELOG.md with 3.6.18 entry

Test plan

• Verify Poi and PoiInput models serialize/deserialize correctly
• Verify Locator model includes new fields without breaking existing usage
• Run make test to confirm all tests pass

🤖 Generated with Claude Code

[github-actions]

📋 Changelog Summary

This PR includes the following changes:

📚 Documentation

• add 3.6.18 changelog entry (ecf936d by @PHKenny, Claude Sonnet 4.6)

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[github-actions]

📊 Test Coverage Report

🎯 Dart/Flutter

Metric	Value
Coverage	11.3%
Lines covered	13636 / 430
Lines missing	-13206

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