feat: initialize blog app with blueprints and templates

Extract blog-specific code from the coop monolith into a standalone
repository. Includes auth, blog, post, admin, menu_items, snippets
blueprints, associated templates, Dockerfile (APP_MODULE=app:app),
entrypoint, and Gitea CI workflow.

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

bp/coop_api.py

@@ -0,0 +1,83 @@
+"""
+Internal JSON API for the coop app.
+
+These endpoints are called by other apps (market, cart) over HTTP
+to fetch Ghost CMS content and menu items without importing blog services.
+"""
+from __future__ import annotations
+
+from quart import Blueprint, g, jsonify
+from sqlalchemy import select
+from sqlalchemy.orm import selectinload
+
+from models.menu_item import MenuItem
+from suma_browser.app.csrf import csrf_exempt
+
+
+def register() -> Blueprint:
+    bp = Blueprint("coop_api", __name__, url_prefix="/internal")
+
+    @bp.get("/menu-items")
+    @csrf_exempt
+    async def menu_items():
+        """
+        Return all active menu items as lightweight JSON.
+        Called by market and cart apps to render the nav.
+        """
+        result = await g.s.execute(
+            select(MenuItem)
+            .where(MenuItem.deleted_at.is_(None))
+            .options(selectinload(MenuItem.post))
+            .order_by(MenuItem.sort_order.asc(), MenuItem.id.asc())
+        )
+        items = result.scalars().all()
+
+        return jsonify(
+            [
+                {
+                    "id": mi.id,
+                    "post": {
+                        "title": mi.post.title if mi.post else None,
+                        "slug": mi.post.slug if mi.post else None,
+                        "feature_image": mi.post.feature_image if mi.post else None,
+                    },
+                }
+                for mi in items
+            ]
+        )
+
+    @bp.get("/post/<slug>")
+    @csrf_exempt
+    async def post_by_slug(slug: str):
+        """
+        Return a Ghost post's key fields by slug.
+        Called by market app for the landing page.
+        """
+        from suma_browser.app.bp.blog.ghost_db import DBClient
+
+        client = DBClient(g.s)
+        posts = await client.posts_by_slug(slug, include_drafts=False)
+
+        if not posts:
+            return jsonify(None), 404
+
+        post, original_post = posts[0]
+
+        return jsonify(
+            {
+                "post": {
+                    "id": post.get("id"),
+                    "title": post.get("title"),
+                    "html": post.get("html"),
+                    "custom_excerpt": post.get("custom_excerpt"),
+                    "feature_image": post.get("feature_image"),
+                    "slug": post.get("slug"),
+                },
+                "original_post": {
+                    "id": getattr(original_post, "id", None),
+                    "title": getattr(original_post, "title", None),
+                },
+            }
+        )
+
+    return bp