feat(fc3b): /api/platforms blueprint (read-only registry view)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/__init__.py

@@ -22,6 +22,7 @@ def all_blueprints() -> list[Blueprint]:
     from .gallery import gallery_bp
     from .import_admin import import_admin_bp
     from .ml_admin import ml_admin_bp
+    from .platforms import platforms_bp
     from .provenance import provenance_bp
     from .settings import settings_bp
     from .showcase import showcase_bp
@@ -44,4 +45,5 @@ def all_blueprints() -> list[Blueprint]:
         aliases_bp,
         ml_admin_bp,
         sources_bp,
+        platforms_bp,
     ]

backend/app/api/platforms.py

@@ -0,0 +1,12 @@
+"""FC-3b: /api/platforms — informational, no auth, matches GS shape."""
+
+from quart import Blueprint, jsonify
+
+from ..services.platforms import PLATFORMS, to_dict
+
+platforms_bp = Blueprint("platforms", __name__, url_prefix="/api/platforms")
+
+
+@platforms_bp.route("", methods=["GET"])
+async def list_platforms():
+    return jsonify({"platforms": {k: to_dict(v) for k, v in PLATFORMS.items()}})