feat(model-manager): flag Early Access models in CivitAI browse

CivitAI Early Access versions require purchased access and otherwise fail
with 401. Surface version `availability` from the API as an `early_access`
flag (per card and per version), show an amber "EARLY ACCESS" tag on the
card, label such entries in the version dropdown, and warn before
attempting to download one.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

model-manager/app/registries.py

@@ -176,6 +176,12 @@ def _pick_thumbnail(version: dict) -> Optional[dict]:
     return None
 
 
+def _is_early_access(version: dict) -> bool:
+    """A version is early-access (download requires purchase/login) when its
+    availability is anything other than Public."""
+    return (version.get("availability") or "Public") != "Public"
+
+
 def _to_card(item: dict) -> dict:
     versions = item.get("modelVersions") or []
     v0 = versions[0] if versions else {}
@@ -192,8 +198,14 @@ def _to_card(item: dict) -> dict:
         "thumbnail": thumb.get("url") if thumb else None,
         "thumbnail_type": thumb.get("type") if thumb else None,
         "primary_version_id": v0.get("id"),
+        "early_access": _is_early_access(v0),
         "versions": [
-            {"id": v.get("id"), "name": v.get("name")} for v in versions
+            {
+                "id": v.get("id"),
+                "name": v.get("name"),
+                "early_access": _is_early_access(v),
+            }
+            for v in versions
         ],
     }