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/browser/templates/social/meta_base.html

@@ -0,0 +1,54 @@
+{# social/meta_base.html — common, non-conflicting head tags #}
+{# Expected context:
+   site: { title, url, logo, default_image, twitter_site, fb_app_id, description? }
+   request: Quart request (for canonical derivation)
+   robots_override: optional string ("index,follow" / "noindex,nofollow")
+#}
+
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+
+{# Canonical #}
+{% set _site_url = site().url.rstrip('/') if site and site().url else '' %}
+{% set canonical = (
+    request.url if request and request.url
+    else (_site_url ~ request.path if request and _site_url else _site_url or None)
+) %}
+
+{# Robots: allow override; default to index,follow #}
+<meta name="robots" content="{{ robots_override if robots_override is defined else 'index,follow' }}">
+
+{# Theme & RSS #}
+<meta name="theme-color" content="#ffffff">
+{% if _site_url %}
+  <link rel="alternate" type="application/rss+xml"
+        title="{{ site().title if site and site().title else 'RSS' }}"
+        href="{{ _site_url }}/rss.xml">
+{% endif %}
+
+{# JSON-LD: Organization & WebSite are safe on all pages (don't conflict with BlogPosting) #}
+{% set org_jsonld = {
+  "@context": "https://schema.org",
+  "@type": "Organization",
+  "name": site().title if site and site().title else "",
+  "url": _site_url if _site_url else None,
+  "logo": site().logo if site and site().logo else None
+} %}
+<script type="application/ld+json">
+{{ org_jsonld | tojson }}
+</script>
+
+{% set website_jsonld = {
+  "@context": "https://schema.org",
+  "@type": "WebSite",
+  "name": site().title if site and site().title else "",
+  "url": _site_url if _site_url else canonical,
+  "potentialAction": {
+    "@type": "SearchAction",
+    "target": (_site_url ~ "/search?q={query}") if _site_url else None,
+    "query-input": "required name=query"
+  }
+} %}
+<script type="application/ld+json">
+{{ website_jsonld | tojson }}
+</script>

shared/browser/templates/social/meta_site.html

@@ -0,0 +1,25 @@
+{# social/meta_site.html — generic site/page meta #}
+{% include 'social/meta_base.html' %}
+
+{# Title/description (site-level) #}
+{% set description = site().description or '' %}
+
+<title>{{ base_title }}</title>
+{% if description %}<meta name="description" content="{{ description }}">{% endif %}
+{% if canonical %}<link rel="canonical" href="{{ canonical }}">{% endif %}
+
+{# Open Graph (website) #}
+<meta property="og:site_name" content="{{ site().title if site and site().title else '' }}">
+<meta property="og:type" content="website">
+<meta property="og:title" content="{{ base_title }}">
+{% if description %}<meta property="og:description" content="{{ description }}">{% endif %}
+{% if canonical %}<meta property="og:url" content="{{ canonical }}">{% endif %}
+{% if site and site().default_image %}<meta property="og:image" content="{{ site().default_image }}">{% endif %}
+{% if site and site().fb_app_id %}<meta property="fb:app_id" content="{{ site().fb_app_id }}">{% endif %}
+
+{# Twitter (website) #}
+<meta name="twitter:card" content="{{ 'summary_large_image' if site and site().default_image else 'summary' }}">
+{% if site and site().twitter_site %}<meta name="twitter:site" content="{{ site().twitter_site }}">{% endif %}
+<meta name="twitter:title" content="{{ base_title }}">
+{% if description %}<meta name="twitter:description" content="{{ description }}">{% endif %}
+{% if site and site().default_image %}<meta name="twitter:image" content="{{ site().default_image }}">{% endif %}