Add unit tests for localizations and improve AI documentation

[Andx667]

Description

This pull request introduces several important improvements to project policies, documentation, and testing infrastructure for the Simplications Flutter app. The main focus is on formalizing build number policies for both human and AI contributors, clarifying localization and persistence requirements, and significantly expanding automated test coverage for core features.

Key changes include:

Policy and Documentation Updates

• Added AGENTS.md as the definitive policy file for AI agents, specifying that any change to core app files under lib/ requires incrementing the build number in pubspec.yaml, and detailing what constitutes a core file and how to bump the version. ([AGENTS.mdR1-R132](https://github.com/tucmi/simplications/pull/5/files#diff-a54ff182c7e8acf56acfd6e4b9c3ff41e2c41a31c9b211b2deb9df75d9a478f9R1-R132))
• Updated .llmrc to clarify the precedence of AGENTS.md, document the build number policy for LLM edits, reflect the now-active multi-language UI and SharedPreferences-based persistence, and update submission and QA checklists to require localization across all supported locales. ([[1]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dR5-R15), [[2]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dL117-R131), [[3]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dL141-R154), [[4]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dL183-R196), [[5]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dL222-R235), [[6]](https://github.com/tucmi/simplications/pull/5/files#diff-1a218f851ad253f775831920fc9e3f8d6f27e8cc162940fa7620dcb48bfa244dL263-R277))
• Added a "Build Number Policy" section to CONTRIBUTING.md, reinforcing the requirement for version bumps on any core file changes and cross-referencing the new AGENTS.md policy. ([CONTRIBUTING.mdR96-R111](https://github.com/tucmi/simplications/pull/5/files#diff-eca12c0a30e25b4b46522ebf89465a03ba72a03f540796c979137931d8f92055R96-R111))

Versioning

• Incremented the build number in pubspec.yaml from 1.0.0+1 to 1.0.0+2 to comply with the new policy after core file changes. ([pubspec.yamlL20-R20](https://github.com/tucmi/simplications/pull/5/files#diff-8b7e9df87668ffa6a04b32e1769a33434999e54ae081c52e5d943c541d4c0d25L20-R20))

Automated Testing

• Added comprehensive new tests for localization fallback and parameter substitution (test/app_localizations_test.dart), device risk scoring logic (test/device_risk_scoring_test.dart), language controller persistence and locale switching (test/language_controller_test.dart), and summary screen rendering and logic (test/summary_screen_test.dart). ([[1]](https://github.com/tucmi/simplications/pull/5/files#diff-9cd14444d1f8095a3a26052974d6ebfb59f4855a3df769b2a3dc8e7c7821f0f0R1-R57), [[2]](https://github.com/tucmi/simplications/pull/5/files#diff-931e43dced578414b91d5611b2bb5ad0b7ae5f0b764a915e5e1f6058a9caf09bR1-R109), [[3]](https://github.com/tucmi/simplications/pull/5/files#diff-ae093e72975e779f5fd136508e3045c6a5ada814b7a17eec91154e4499e04ec5R1-R55), [[4]](https://github.com/tucmi/simplications/pull/5/files#diff-3231ed26d662f7813efde3bff889603cedd59ecbabae17e0e47a663c3897888aR1-R83))

These changes collectively improve project maintainability, ensure consistent versioning for releases, and increase confidence in core app functionality through robust automated testing.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation
• Other:

Checklist

• flutter analyze passes with no new issues
• flutter test passes
• New or updated strings have translations in all supported locales
• Self-reviewed the diff