[US-07]User can propose a swap with fairness indicator

[ChatGPT486]

Field	Details
As a	Registered user
I want to	Propose one of my items in exchange and see a fairness
	indicator comparing item values
So that	Both parties can assess if the swap is balanced
Story Points	8
Sprint	Sprint 2
Priority	High

Acceptance Criteria:

• User can click "Propose Swap" on any item detail page
• User selects which of their own items to offer
• Fairness indicator shows value comparison between items
• User can add an optional message with the proposal
• Proposal is sent and owner is notified
• Proposal appears in both users' dashboards

Labels: priority: high | type: user-story | sprint-2
Milestone: Sprint 2 — Marketplace & Swap Flow