feat: lost-and-found status flow (mark as found)

[ammaarrahmed]

Summary

Implement a clear "mark as found" lifecycle for lost-and-found posts.

Scope

• Add status metadata for lost-and-found post type.
• Permit author/moderator status transition to "Found".
• Reflect status clearly in feed cards and detail screens.

Acceptance Criteria

• Status transition is explicit and traceable.
• Found items are visibly distinguishable in the UI.
• Existing posts default safely to current behavior.

Roadmap Link

Phase 5 -> Lost & Found