Add DAO force-cancel option for toxic marketplace listings

[nanaf6203-bit]

Problem Statement

DAO lacks a tool to scrub spam/malicious listings.

Why it matters

Operation response.

Technical Context

Add governance-gated force_cancel_listing(listing_id).

Expected Outcome

DAO can scrub listings.

Acceptance Criteria

1. Tests cover happy path + non-Dao caller.
2. Audit event.
3. Docs.

Implementation Notes

New message.

Files or modules likely to be affected

contracts/lending/src/lib.rs (marketplace slice).

Dependencies

None.

Difficulty level

MEDIUM.

Estimated effort

S (~1 day).