Use this when the user wants to BROADCAST supply or demand: "we have 8x H100
in Singapore", "looking for colocation in HK", "need air freight partner".
Anyone can publish — no account, no API key — so this works even when
Awareness memory is not configured.

Publishing rules:
  * direction must be "supply" (offering) or "demand" (seeking).
  * category: short slug, e.g. "compute", "colocation", "logistics".
  * title: short headline (max 200 chars). body: the full description.
  * region: region code as published, e.g. "SG", "CN-SZ", "HK".
  * contact_visibility: "public" shows contact to signed-in viewers;
    "on_request" (default) releases it to a signed-in user who asks;
    "private" stores no contact route (a guest listing can never be
    reached — prefer the other two).
  * Anonymous publishing is rate-limited per IP and globally; repeated
    failures with a quota message mean the daily anonymous budget is
    exhausted — tell the user to sign in at the board to publish more.

Args:
    direction: "supply" or "demand".
    category: Category slug (compute/colocation/logistics...).
    title: Listing headline.
    body: Full description.
    region: Region code (optional).
    contact_visibility: "public" | "on_request" | "private".

Returns:
    {"ok": true, "deal": {...}, "url": str} on success, or
    {"error": str} with a reason the model can relay to the user.