POC: clean architecture v2 (multichoice_v2 + application/data/domain)

[ZanderCowboy]

Summary

• Draft POC exploring a clean-architecture split using packages/domain, packages/application, and packages/data.
• Introduces a separate app target at apps/multichoice_v2/ to avoid breaking the existing apps/multichoice app.
• Adds a reference guide at CLEAN_ARCHITECTURE_GUIDE.md describing the intended layering and dependency rules.

Details

• UI layer: apps/multichoice_v2/ (intentionally isolated, minimal wiring)
• Application layer: packages/application/ (use case implementations)
• Domain layer: packages/domain/ (entities + repository/use case interfaces)
• Data layer: packages/data/ (repository implementations + Isar/local datasources + mappers)

What changed in this refresh

• Synced the branch content to the remote PR branch and made the POC compile/analyze cleanly.
• Made domain and application Flutter-free (uses lints), matching the guide’s dependency direction.
• Aligned the POC data layer to the repo’s Isar convention (isar_community).
• Ran codegen for the new POC packages so generated files exist.

Test plan

• melos run get
• melos analyze

Notes / Risks

• This PR remains a conceptual WIP; it does not migrate the existing app.
• IDs/entities in the POC are still evolving (this is not a finalized architecture).

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
94.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.23%. Comparing base (93bd56d) to head (6cc2f60).
⚠️ Report is 15 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #227      +/-   ##
===========================================
+ Coverage    82.19%   83.23%   +1.03%     
===========================================
  Files           49       49              
  Lines         1556     1533      -23     
===========================================
- Hits          1279     1276       -3     
+ Misses         277      257      -20     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
83.7% Coverage on New Code
0.9% Duplication on New Code

See analysis details on SonarQube Cloud