Fix compile-time error in FeedRepository.updatePost payload construction

[syed-reza98]

Why

FeedRepository.updatePost() currently constructs a Dart map using invalid syntax (?location, ?taggedPetIds, etc.), which breaks compilation.

Where

• lib/repositories/feed_repository.dart → updatePost(...)

Tasks

• Replace invalid map entries with conditional keys:
  • Always include caption
  • Include location only when non-null and non-empty
  • Include tagged_pet_ids / tagged_pet_names only when provided and consistent
• Ensure omission does not clear existing DB values unintentionally

Acceptance criteria

• flutter analyze passes
• App builds and runs
• Updating caption/location/tags works without errors

References

• Stability requirement in docs/02_FEATURES_REQUIREMENTS_BEST_PRACTICES.md (error handling + maintainability)
• Repo lib/ review identified this as a build-breaking defect.

[syed-reza98]

Closed as completed via PR #71.