feat(operator): VM marketplace — Phase A registry + Phase B trading

Phase A: host-global VM registry (~/.hh/registry.json) joining opaque
snapshots to their .hh-agent manifests. New src/registry.rs (serde_json),
one Entry per saved VM with cached purpose/status/todo scraped from the
live container at save time. Reconcile-on-read self-evicts pruned images.
/sbx browse TUI lister + operator-side `registry list|show` reader.

Phase B: trading/skill VMs. Entry gains shareable/tags/share_path +
publish/get/list_shareable helpers. New TUI verbs /sbx publish <label>
[tag...], /sbx catalog @user, /sbx pull @user <label>. Wire protocol adds
_sbx:catreq/catalog/pullreq frames (parse_sbx). Receiver auto-loads a
received hh-snap-*.tar, reads the in-image manifest, and self-registers
(kept shareable for re-trade). Reuses the existing E2E /send + ft.rs
streaming transport.

podman gotcha fixed: `podman load` prints registry-qualified
`localhost/hh-snap:<label>` vs docker's bare tag — parse_loaded_tag now
finds the hh-snap: marker anywhere in the line (unit-tested both shapes).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hh/src/main.rs

@@ -9,6 +9,7 @@ mod crypto;
 mod ft;
 mod layout;
 mod net;
+mod registry;
 mod sbx;
 mod theme;
 mod ui;