feat: extract shared infrastructure from shared_lib

Phase 1-3 of decoupling plan:
- Shared DB, models, infrastructure, browser, config, utils
- Event infrastructure (domain_events outbox, bus, processor)
- Structured logging
- Generic container concept (container_type/container_id)
- Alembic migrations for all schema changes

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

browser/templates/macros/title.html

@@ -0,0 +1,10 @@
+{% macro title(_class='') %}
+  <a
+    href="{{ coop_url('/') }}"
+    class="{{_class}}"
+  >
+  <h1>
+    {{ site().title }}
+  </h1>
+  </a>
+{% endmacro %}