feat(platform): objectstore port — local + GCS adapters, config (SD-0002 §6.2)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/platform/config.py

@@ -68,3 +68,31 @@ def smtp_from() -> str:
 def smtp_starttls() -> bool:
     """STARTTLS on the relay connection (default on; disable only for odd relays)."""
     return os.environ.get("ECOMM_SMTP_STARTTLS", "1").strip().lower() not in {"0", "false", "no", "off"}
+
+
+def objectstore_kind() -> str:
+    """Which objectstore adapter to build: 'local' (dev/tests) or 'gcs' (deployed)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_KIND") or "local"
+
+
+def objectstore_bucket() -> str:
+    """The GCS bucket name for the media objects (gcs adapter; deployment overlay)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_BUCKET", "")
+
+
+def objectstore_local_dir() -> str:
+    """Base directory for the local-disk objectstore adapter (dev/tests)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_DIR") or "/tmp/ecomm-objectstore"
+
+
+def public_base_url() -> str:
+    """Absolute origin for hosted image URLs in export (e.g. APP_URL); '' → relative."""
+    return (os.environ.get("APP_URL") or "").rstrip("/")
+
+
+def image_fetch_allow_private() -> bool:
+    """Allow image fetch from private/loopback hosts (dev/E2E fixture host only).
+    Default off — the SSRF guard rejects private ranges in deployed envs."""
+    return os.environ.get("ECOMM_IMAGE_FETCH_ALLOW_PRIVATE", "").strip().lower() in {
+        "1", "true", "yes", "on",
+    }