Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

shared/services/widget_registry.py

@@ -0,0 +1,90 @@
+"""Singleton widget registry for cross-domain UI composition.
+
+Usage::
+
+    from shared.services.widget_registry import widgets
+
+    # Register at app startup (after domain services)
+    widgets.add_container_nav(NavWidget(...))
+
+    # Query in templates / context processors
+    for w in widgets.container_nav:
+        ctx = await w.context_fn(session, container_type="page", ...)
+"""
+from __future__ import annotations
+
+from shared.contracts.widgets import (
+    NavWidget,
+    CardWidget,
+    AccountPageWidget,
+    AccountNavLink,
+)
+
+
+class _WidgetRegistry:
+    """Central registry holding all widget descriptors.
+
+    Widgets are added at startup and read at request time.
+    Properties return sorted-by-order copies.
+    """
+
+    def __init__(self) -> None:
+        self._container_nav: list[NavWidget] = []
+        self._container_card: list[CardWidget] = []
+        self._account_pages: list[AccountPageWidget] = []
+        self._account_nav: list[AccountNavLink] = []
+
+    # -- registration ---------------------------------------------------------
+
+    def add_container_nav(self, w: NavWidget) -> None:
+        self._container_nav.append(w)
+
+    def add_container_card(self, w: CardWidget) -> None:
+        self._container_card.append(w)
+
+    def add_account_page(self, w: AccountPageWidget) -> None:
+        self._account_pages.append(w)
+        # Auto-create a matching internal nav link
+        slug = w.slug
+
+        def _href(s=slug):
+            from shared.infrastructure.urls import account_url
+            return account_url(f"/{s}/")
+
+        self._account_nav.append(AccountNavLink(
+            label=w.label,
+            order=w.order,
+            href_fn=_href,
+            external=False,
+        ))
+
+    def add_account_link(self, link: AccountNavLink) -> None:
+        self._account_nav.append(link)
+
+    # -- read access (sorted copies) ------------------------------------------
+
+    @property
+    def container_nav(self) -> list[NavWidget]:
+        return sorted(self._container_nav, key=lambda w: w.order)
+
+    @property
+    def container_cards(self) -> list[CardWidget]:
+        return sorted(self._container_card, key=lambda w: w.order)
+
+    @property
+    def account_pages(self) -> list[AccountPageWidget]:
+        return sorted(self._account_pages, key=lambda w: w.order)
+
+    @property
+    def account_nav(self) -> list[AccountNavLink]:
+        return sorted(self._account_nav, key=lambda w: w.order)
+
+    def account_page_by_slug(self, slug: str) -> AccountPageWidget | None:
+        for w in self._account_pages:
+            if w.slug == slug:
+                return w
+        return None
+
+
+# Module-level singleton — import this everywhere.
+widgets = _WidgetRegistry()