Add coop fragment middleware and env vars

Fetch nav-tree, auth-menu, cart-mini from coop apps for unified
header. Add INTERNAL_URL env vars for Docker networking. Update
base.html to render fragment blocks.

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

app/__init__.py

@@ -10,6 +10,7 @@ from fastapi import FastAPI, Request
 from fastapi.responses import JSONResponse, HTMLResponse
 
 from artdag_common import create_jinja_env
+from artdag_common.middleware.auth import get_user_from_cookie
 
 from .config import settings
 
@@ -37,6 +38,44 @@ def create_app() -> FastAPI:
         lifespan=lifespan,
     )
 
+    # Coop fragment pre-fetch — inject nav-tree, auth-menu, cart-mini
+    _FRAG_SKIP = ("/auth/", "/.well-known/", "/health",
+                   "/internal/", "/static/", "/inbox")
+
+    @app.middleware("http")
+    async def coop_fragments_middleware(request: Request, call_next):
+        path = request.url.path
+        if (
+            request.method != "GET"
+            or any(path.startswith(p) for p in _FRAG_SKIP)
+            or request.headers.get("hx-request")
+        ):
+            request.state.nav_tree_html = ""
+            request.state.auth_menu_html = ""
+            request.state.cart_mini_html = ""
+            return await call_next(request)
+
+        from artdag_common.fragments import fetch_fragments as _fetch_frags
+
+        user = get_user_from_cookie(request)
+        auth_params = {"email": user.email} if user and user.email else {}
+        nav_params = {"app_name": "artdag", "path": path}
+
+        try:
+            nav_tree_html, auth_menu_html, cart_mini_html = await _fetch_frags([
+                ("blog", "nav-tree", nav_params),
+                ("account", "auth-menu", auth_params or None),
+                ("cart", "cart-mini", None),
+            ])
+        except Exception:
+            nav_tree_html = auth_menu_html = cart_mini_html = ""
+
+        request.state.nav_tree_html = nav_tree_html
+        request.state.auth_menu_html = auth_menu_html
+        request.state.cart_mini_html = cart_mini_html
+
+        return await call_next(request)
+
     # Initialize Jinja2 templates
     template_dir = Path(__file__).parent / "templates"
     app.state.templates = create_jinja_env(template_dir)